Routing using segment-based metrics

ABSTRACT

A router advertises an aggregated service or route that can be evaluated by other routers as a unitary segment rather than as a group of individual links/paths associated with the aggregated service or route. The aggregated service or route can be based on service and topology state information received from one or more other routers and can be advertised with the router as the nexthop for the aggregated service or route. The router can advertise an aggregated metric for the aggregated service or route for use in such evaluation. An aggregated route can be associated with different aggregated metrics for different services.

This application is a continuation of U.S. patent application Ser. No.17/245,898 filed Apr. 30, 2021, which is a continuation of U.S. patentapplication Ser. No. 16/410,121, filed May 13, 2019, entitled “ROUTINGUSING SEGMENT-BASED METRICS,” now U.S. Pat. No. 10,999,182, issued May4, 2021, the entire content of each application is incorporated hereinby reference.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This patent application is related to U.S. patent application Ser. No.15/054,781, filed Feb. 26, 2016 (now issued U.S. Pat. No. 9,985,883),entitled “NAME-BASED ROUTING SYSTEM AND METHOD, the entire content ofwhich is herein incorporated by reference.

This patent application also is related to U.S. patent application Ser.No. 14/833,571, filed Aug. 24, 2015 (now issued U.S. Pat. No.9,762,485), entitled “NETWORK PACKET FLOW CONTROLLER WITH EXTENDEDSESSION MANAGEMENT,” the entire content of which is herein incorporatedby reference.

TECHNICAL FIELD

The disclosure generally relates to routing using segment-based metrics.

BACKGROUND

A routing platform such as the 128T routing platform from 128 Technologyof Burlington, MA can be considered service-oriented, in that theservice configuration is the focal point of the data model (and hencethe configuration paradigm). In such service-oriented routing platforms,administrators may define services to represent the capabilities thattheir network is designed to deliver to consumers, and theseservices—along with their requisite policies and characteristics—dictatehow the traffic patterns traverse the network.

The 128T routing platform is comprised of two primary components: theSession Smart Router (SSR) and the Conductor. Together, the SSR andConductor form a single logical control plane that is highlydistributed, and a data plane that is truly session-aware. The SSRcombines a service-centric control plane and a session-aware data planeto offer all IP routing tables, feature-rich policy management, advanceddata collection, and analytics in addition to high-speed packetforwarding, classification, and security functions. The Conductor is acentralized management and policy engine that provides orchestration,administration, zero-touch provisioning, monitoring, and analytics fordistributed SSRs—while maintaining a network-wide, multi-tenant service,and policy data model. Through these components, the 128T routingplatform supports a wide range of deployment models scaling from a smallbranch office to a high capacity edge router to a hyper-scalesoftware-defined data center.

To date, the notion of services has been limited to a single “router”(collection of nodes), or exported to external routers using explicitconfiguration, through the use of the Conductor. This can make itdifficult to extend service configuration to a large number of SSRs.

SUMMARY

In accordance with one embodiment of the invention, a routing systemcomprises a first router and a second router, wherein the first routeris configured to receive service and topology state information for atleast one other router; identify, using the received service andtopology state information, a route or service from another router forwhich access to the route or service is available to the second routerthrough the first router; compute an aggregated metric for the route orservice available through the first router; and publish the route orservice to the second router including the aggregated metric and thefirst router as the nexthop for the published route or service.

In accordance with another embodiment, a router comprises a datastoreand a service and topology exchange protocol (STEP) client controllerconfigured to receive service and topology state information for atleast one other router and store the received service and topology stateinformation in the datastore; identify, using the received service andtopology state information, a route or service from another router forwhich access to the route or service is available to a second routerthrough the first router; compute an aggregated metric for the route orservice available through the router; and publish the route or serviceto the second router including the aggregated metric and the router asthe nexthop for the published route or service.

In various alternative embodiments of the above-mentioned routing systemand router, the first router may publish the route or service bytransmitting the route or service to a central repository that isconfigured to convey the route or service to the second router. Thefirst router may be a member of a first district and a second district,the second router may be a member of the second district, the firstrouter may receive the service and topology state information from atleast one other router in the first district, and the first router maypublish the route or service to the second router in the second districtin a manner that hides, from the second router, information from thefirst district relating to the route or service. The route or servicemay be in the first district or may be in a third district. The firstdistrict may be associated with a first district name and the firstrouter may be configured to publish the route or service to the secondrouter in the second district including a source path for the publishedroute or service with the first district name included in the sourcepath. The first router may be configured to receive the published routeor service including the source path from another district and to appendthe first district name to the source path.

In accordance with another embodiment, a routing system for detectingand avoiding loops between a plurality of routers organized into aplurality of districts comprises a plurality of routers organized into aplurality of districts including at least a first district and a seconddistrict, each district associated with a distinct district name, theplurality of routers including a first router that is a member of thefirst district and the second district, the first router configured topublish a first route or service from the first district to the seconddistrict by transmitting a first publication including the first routeor service and a first source path for the first route or service withthe first district name included in the first source path; receive fromanother district a second publication of a second route or serviceincluding a second source path; determine if the second source pathincludes the first district name; process the second route or service asa newly learned route or service in the first district when the secondsource path does not include the first district name; and ignore thesecond route or service when the second source path does include thefirst district name.

In another exemplary embodiment, a router for detecting and avoidingloops between a plurality of routers organized into a plurality ofdistricts including at least a first district and a second district,each district associated with a distinct district name, the router beinga member of the first district and the second district. The routercomprises a controller configured to publish a first route or servicefrom the first district to the second district by transmitting a firstpublication including the first route or service and a first source pathfor the first route or service with the first district name included inthe first source path; receive from another district a secondpublication of a second route or service including a second source path;determine if the second source path includes the first district name;process the second route or service as a newly learned route or servicein the first district when the second source path does not include thefirst district name; and ignore the second route or service when thesecond source path does include the first district name.

In various alternative embodiments of the above-mentioned routing systemand router, the first route or service published by the first router mayidentify the first router as a nexthop for the first route or service inthe first district. Publishing the first route or service from the firstdistrict to the second district may involve receiving the firstpublication from another district including the first source path andappending the first district name to the first source path in the firstpublication. The first router may transmit the first publication to acentral repository that is configured to convey the route or service toat least one router in the second district and may receive the secondpublication from the central repository.

Additional embodiments may be disclosed and claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

Those skilled in the art should more fully appreciate advantages ofvarious embodiments of the invention from the following “Description ofIllustrative Embodiments,” discussed with reference to the drawingssummarized immediately below.

FIG. 1 is a schematic diagram showing major components of the STEPserver 100, in accordance with one exemplary embodiment.

FIG. 2 is a logic flow diagram for the STEP server controller 120 inimplementing the high-level STEP server functions, in accordance withone exemplary embodiment.

FIG. 3 is a schematic diagram showing major components of the STEPclient 300, in accordance with one exemplary embodiment.

FIG. 4 is a logic flow diagram for the STEP client controller 220 inimplementing the high-level STEP client functions, in accordance withone exemplary embodiment.

FIG. 5 is a schematic diagram showing an exemplary topology segmented asone district with multiple neighborhoods.

FIG. 6 is a schematic diagram showing the same topology as FIG. 5 butsegmented into multiple districts.

FIG. 7 is a schematic diagram showing a topology including two routerspeering with each other.

FIG. 8 is a schematic diagram showing an example of redistributing BGPinto services.

FIG. 9 is a schematic diagram showing an example of redistributing BGPinto STEP.

FIG. 10 is a schematic diagram showing a topology including a multicastconfiguration with no receivers.

FIG. 11 is a schematic diagram showing the topology of FIG. 10 but nowwith router R2 having received IGMP joins on two of its interfaces.

FIG. 12 is a schematic diagram showing the same topology as FIG. 6 .

FIG. 13 is a schematic diagram showing a topology including a serviceexchange between districts that causes a loop.

FIG. 14 is a schematic diagram showing the topology of FIG. 13 butincluding service exchange between districts with loop avoidance.

FIG. 15 is a schematic diagram showing a topology including source basedrouting within the same district.

FIG. 16 is a schematic diagram showing a topology including source basedrouting across multiple districts.

FIG. 17 is a schematic wire frame diagram showing a heatmap view of thenetwork.

FIG. 18 is a logic flow diagram for publishing an aggregated route orservice, in accordance with one exemplary embodiment.

FIG. 19 is a logic flow diagram for loop detection and prevention, inaccordance with one exemplary embodiment.

FIG. 20 is a logic flow diagram for source-based routing, in accordancewith an exemplary embodiment.

FIG. 21 is a schematic diagram showing a topology includingpoint-to-multipoint SVR routing.

FIG. 22 is a schematic diagram showing a topology including multicastproxy routing.

It should be noted that the foregoing figures and the elements depictedtherein are not necessarily drawn to consistent scale or to any scale.Unless the context otherwise suggests, like elements are indicated bylike numerals.

DETAILED DESCRIPTION Definitions

As used in this description and the accompanying claims, the followingterms shall have the meanings indicated, unless the context otherwiserequires:

STEP stands for Service and Topology Exchange Protocol, which is used todescribe various mechanisms for distributing various types of serviceand topology state information among and between routers and for usingsuch distributed service and topology state information in makingintelligent routing decisions.

Authority is a single administrative domain that is comprised of acollection of routers; generally analogous to an Autonomous System (AS)in a BGP network. An authority can be a single network, a collection ofnetworks, or single managed entity for a group of routers. In anexemplary embodiment, authorities are named with text strings. Authoritynames are unique and may be assigned/managed by a naming authority orother technique that guarantees uniqueness. In exemplary embodiments, aprivate naming authority is used, although in alternative embodiments apublic naming authority (e.g., IANA or equivalent) may be used. In anexemplary embodiment, authority names are resource names that conform toRFC 1737.

Neighborhood is an IP network of reachability. All router interfacesconfigured to be within the same neighborhood are expected to bemutually reachable. This includes interfaces separated by networkboundaries, NATs, and firewalls but are mutually reachable. In exemplaryembodiments, a neighborhood is a label (string value) applied to anetwork interface that describes desired connectivity (peeringrelationships) between routers. Any two router interfaces within anAuthority that share at least one neighborhood label are presumed to beconnected to a common L3 network that intends those two interfaces to becapable of reaching one another. Assigning two interfaces to the sameneighborhood causes the routers to create a peering relationship withone another. In an exemplary embodiment, every network interface on anSSR belongs to at least one neighborhood, and if a network interface isleft unconfigured by the administrator, the SSR will automaticallyassign it a neighborhood name that is unique among all interfaces withinthe Authority. A network interface can be a member of multipleneighborhoods and can contain a user-ordered list of neighborhoods thatall describe the same non-unique L3 network. In this context, a userordered list specifies the ordering of the neighborhoods, where thefirst neighborhood listed will be considered the “primary” neighborhood,and will be the neighborhood associated with all inbound sessionsarriving on that network interface for purposes of analytics data,redundancy state information, and other interface-specific metrics. Twonetwork interfaces belonging to the same neighborhood are effectivelytreated as having a direct neighbor relationship, even if thecommunication path between the two network interfaces passes through oneor more other routers. In an exemplary embodiment, in order to constrainwhich interfaces attempt to peer with one another and to avoidunnecessary peering relationships, each interface's neighborhood can beassigned a topology type as either mesh, hub, or spoke, where a meshinterface attempts to peer with all other neighborhood interface of typemesh or hub, a hub interface attempts to peer with all otherneighborhood interfaces of type mesh, and a spoke interface attempts topeer with all other neighborhood interfaces of type mesh or hub.

District is essentially a collection of neighborhoods. Every routerparticipating in a district will receive link state metrics about everyother router interface within the same district. This information can beused to aggregate service state availability to other districts.

A “Tenant” is a single sub-network that is to be segregated andseparated from all others, e.g., for security, manageability, andanalytics. This is akin to VLAN or VxLAN or VRF. A Tenant is a textstring assigned by an Authority or parent Tenant.

A “Service” is a single named application and is the target of a route.This is similar to an IP address after DNS resolution or CIDR block. AService is named with a text string that normally matches the URL of aservice. A Service is represented by a text string that is used withinthe routing protocol.

A “Service Group” is a portion of a sub-network (Tenant) that is to besegregated, e.g., for manageability and analytics. A Service Group isrepresented by a text string that is used within the routing protocol.

A “Qualified Service Name” or “QSN” is an addressable resource. This isa textual representation of a tenant, a service-group, or a service. Inan exemplary embodiment, every QSN has one unique Authority and uses URIGeneric Syntax defined by RFC 3986 in the formQSN://Subtenant.Tenant.Authority/ServiceGroup/Service. Service Groupsare optional, and should they not be used, the QSN can be shortened tonot include this text. Some exemplary embodiments of QSNs, tenants,service-groups, and services are described in related U.S. patentapplication Ser. No. 15/054,781 filed Feb. 26, 2016 (now issued U.S.Pat. No. 9,985,883), which was incorporated by reference above.

SVR stands for Secure Vector Routing. This is how packets are forwardedbetween two peer SSRs in the 128T routing platform. SVR implementsaspects of session-based routing as described in related U.S. patentapplication Ser. No. 14/833,571, now issued U.S. Pat. No. 9,762,485,which was incorporated by reference above.

A Vector is an attribute of a neighborhood on a given router interface,and can be used by administrators to exert control over the routingdecision logic (path selection) employed by the router. Whereasneighborhoods describe the topology (peering relationships) betweenrouters, vectors describe path preference for service traffic over thattopology. Each neighborhood (within an interface) may contain the nameof a vector, which is a label that allows administrators to ascribe someproperty to that neighborhood for influencing routing. A vector can alsobe thought of as a name for a peering relationship between two routerswithin a neighborhood. Once vectors are configured, administrators mayassign priorities to those vectors within service-policy configurationelements, e.g., a service (via its policy) can indicate a preferred typeof vector or hierarchy of vectors for a particular service. For example,a video conference service might be configured to use an MPLS vector ifavailable and to use a basic Internet path vector otherwise.Furthermore, a service-policy can assert that certain vectors are neverto be used for a given service. For example, an HD video conferenceservice may be unusable or cost-prohibitive when sent over LTE, so in anexemplary embodiment the administrator can assign a priority of “never”to the LTE vector with respect to the HD video service. Additionally oralternatively, vectors can be associated with various metrics (e.g.,cost or performance-based metrics) for use in selecting routes. Forexample, if a network includes vectors A, B, C, D with respective costsof 10, 20, 50, 60 and a route could use either vectors A/C or vectorsB/D, then the router typically would select vectors A/C having anaggregate cost of 60 instead of vectors B/D having an aggregate cost of80. Different routes to a particular destination can be computed byassigning different costs to links for different services, e.g., forpurposes of web traffic, a particular link might have a cost X and forpurposes of email traffic, the link might have a cost Y, such thatroutes for web traffic and for email traffic traverse different pathsthrough the network even if both types of traffic arrive at the sameegress router.

The terms “publish” and “advertise” (and variants thereof) are usedinterchangeably unless the context otherwise requires.

A “set” includes one or more members.

Introduction

In exemplary embodiments, a router advertises an aggregated service orroute that can be evaluated by other routers as a unitary segment ratherthan as a group of individual links/paths associated with the aggregatedservice or route. The aggregated service or route can be based onservice and topology state information received from one or more otherrouters and can be advertised with the router as the nexthop for theaggregated service or route. The router can advertise an aggregatedmetric for the aggregated service or route for use in such evaluation.An aggregated route can be associated with different aggregated metricsfor different services.

Exemplary embodiments are described herein with reference to SessionSmart Routers (SSRs) of the type sold by 128 Technology of Burlington,MA, although it will be understood by those of ordinary skill in the artthat various aspects of the described embodiments can be applied toother networking devices either now or in the future to overcome thetypes of networking and configuration issues described herein.

As discussed above, service configuration of a large number of SSRs canbe difficult. Furthermore, as networks are constantly changing,information regarding services and service reachability needs to beexchanged between SSRs, as network and application state is dynamic. Forexample, service routes are generally configured for services withwell-known destinations-akin to static routes. In some cases, theservices resort to routing in order to learn the nexthops. These routescan be learned in various ways, such as via a traditional routingprotocol (e.g., OSPF, BGP, etc.), via static routes, or via connectedroutes. Each SSR may learn different routes by virtue of runningdifferent routing protocols. Routes need to be eventually applied toservices, applied to applications, and/or distributed to other SSRs. Ifsome routes are withdrawn, some of the services may become unavailable,and this state change needs to be propagated. Furthermore, SSRscurrently do not have visibility into whether a service is available atthe ultimate destination (last hop). This lack of visibility, from anetworking perspective, can lead to incorrect routing of packets.

In exemplary embodiments, routers within a portion of a network (e.g.,within an authority or district as discussed below, up to an includingan entire network) implement a service and topology exchange protocol(referred to herein as STEP) to exchange service and topology stateinformation such that each router in the portion of the network thatparticipates in STEP (referred to hereinafter as a STEP router) obtainsservice and topology state information from all of the other STEProuters in the portion of the network and optionally also from STEProuters outside of the portion of the network. Among other things, STEPallows the STEP routers to propagate network state and network statechanges as well as manage services across routers, e.g., as more routersbecome part of an authority or district. The network can be segmentedinto multiple portions, and a STEP router can be a member of multipleportions, thereby participating in STEP exchanges within each portionfor which it is a member. The STEP routers in one portion can advertiseservices and routes both within the portion and outside of the portion.When advertising a service or route outside of the portion, the serviceor route can be advertised as an aggregated service or route, e.g.,identifying one particular STEP router in the portion through which theservice or route can be accessed and optionally including an aggregatedmetric for the aggregated service or route (e.g., loss, latency, jitter,and/or cost values for the aggregated service or route based on themetrics of individual links/paths associated with the service or routewithin the portion of the network). Among other things, such segmentrouting, e.g., segmenting the network and allowing for advertisement ofaggregated services and routes across network segments, can reduce theamount of information flow needed to distribute the service and topologystate information.

The STEP routers within each portion of the network are typicallyspecified through configured relationships, e.g., specifying which STEProuters belong to a particular authority or district. From theseconfigured relationships, the STEP routers can exchange service andtopology state information directly or indirectly, as discussed furtherbelow. The service and topology state information can includetraditional link—state information (e.g., obtained from a traditionalrouting protocol such as OSPF or BGP) as well as additional informationsuch as service level agreement (SLA) information (e.g., the servicelevel agreement for a particular service, and whether or not the serviceis operating within the service level agreement), path metrics (e.g.,configured link speed, actual computed link speed, link state up/down,jitter, packet loss rate, latency, vector information, and/or costvalues per path/vector), multicast membership and permissioninformation, and other information relevant to making intelligentrouting decisions. Among other things, STEP therefore provides moreinformation to the STEP routers than would be available from atraditional routing protocol alone, allowing each STEP router to makemore intelligent routing decisions including routing packets based onservice level agreement (SLA) and path metrics, making intelligentmulticast routing decisions, and supporting intelligent source routing,to name but a few ways that STEP can be utilized.

In certain exemplary embodiments, STEP is implemented using acentralized distribution system (referred to herein as the STEP serveror STEP repository) for dynamically exchanging service and topologystate information by and between routers so that the routers can makemore intelligent routing decisions. Specifically, each router thatparticipates in STEP (referred to hereinafter as a STEP router)dynamically transmits its own service and topology state information tothe STEP repository and dynamically receives service and topology stateinformation for one or more other STEP routers from the STEP repositorybased on configured relationships between STEP routers. The STEPrepository is managed by a STEP server in any of a variety of networkdevices as discussed below, and each STEP router implements a STEPclient with respect to this client-server model. Certain exemplaryembodiments are described below in the context of this centralizeddistribution system, although it should be noted that STEP can beimplemented using other mechanisms for distributing service and topologystate information, some of which are described herein below.

It should be noted that STEP routers can include SSRs or other routersaugmented with some or all of the STEP functionality described herein.

STEP is being developed to address the following challenges in currentSSR network deployments, although it generally provides a mechanism fordistributing information within the network that can be used for otherpurposes now or in the future:

Interaction with Multiple Routing Protocols

Provisioning is required to configure BGP over SVR between two SSR peersto exchange BGP routes between two SSRs. This does not scale well acrossmultiple SSRs. There is also a need to map the route information fromthese legacy routing protocols into the SSR world of services andservice-routes. STEP provides an easy way to enforce this. It alsoprovides an extensible way to interact with any future legacy protocols(like ISIS, etc.) if needed or desired. With STEP, networkadministrators would be able to plug-in the SSRs with any legacy routersand map them to services and make them available to the whole network.

Multicast

With multicast (e.g., IGMP support), all multicast receivers for a groupare learned by an SSR. With STEP, the receiver endpoints will beadvertised via the STEP repository and the optimalreplication/rendezvous point can be determined to send multicast packetsto all receivers, e.g., the smallest tree needed to distribute themulticast packets.

End Point Availability

It is possible for a far end SSR to route services to another SSR wherethe service is no longer available. Service availability is not justlimited to routes or path states. The final application state could bequeried using health APIs as well and is not limited to just the linkstate alone to determine service state. Currently, SSRs work around thislimitation using path and interface failover techniques that will notwork in all cases, especially when there is total outage and when theservices are unavailable on other routers as well. STEP can propagatethe service availability information across the whole network so thateach router can make intelligent decisions and minimize outages.

Pinpoint Service Outages in the Whole Network

STEP stores the service and topology state information in the STEPrepository. Thus, the STEP repository generally has the whole view ofthe network at any given time, and the STEP repository also can storehistorical information as service and topology state information updatesare received from STEP routers. This current and historical informationcan be used for any of a variety of purposes, such as, for example,troubleshooting service and topology problems, making network managementdecisions (e.g., to shut down a particular router, or to control whatinformation a particular router advertises via the STEP repository), oreven reverting to a prior network state (e.g., by “replaying” a sequenceof network state changes), to name but a few. Service outages orheat-map views of the whole network can be easily generated at any giventime. This helps with fault isolation and enhances the ability to debugnetwork problems.

Scalability

STEP allows the network to easily scale and provides insights into thewhole network. STEP also will help network administrators easily designand scale existing or new networks and provide insight into the serviceavailability across the whole network. In certain exemplary embodiments,there will two manifestations of STEP referred to as “internal STEP” or“iSTEP” and “external STEP” or “eSTEP.” Internal STEP is the protocolused to exchange services within an authority and is the primary focusof the following description. External STEP is the protocol used toexchange services across authorities and is discussed briefly in thefollowing description.

Step Repository

An exemplary embodiment of STEP and the various network elements usedwith STEP is now described.

As discussed above, STEP routers participating in a STEP-enabled networkpublish service and topology state information that is maintained in aSTEP repository by a STEP server. For convenience, the service andtopology state information published by a given STEP router is referredto herein as a STEP document. In specific exemplary embodiments, theSTEP document is a JavaScript Object Notation (JSON) encoded document,although other mechanisms may be used in various alternative embodiments(e.g., HTML or a binary coded document). Service providers also maypublish information to the STEP repository, e.g., to advertise serviceinformation from their networks/authority. The STEP information receivedby the STEP server from the STEP routers and optionally also from theservice providers is selectively distributed to other STEP routers andused by the STEP routers to intelligently route traffic to services andalso react to network changes.

In certain exemplary embodiments, the STEP repository is built upon ahighly efficient and scalable in-memory database that follows apublish-subscribe model, referred to herein as the Path Tree database.In exemplary embodiments, the STEP repository/server performs thecollection and distribution of service and topology state information,and all of the routing decisions (both client publishing routing dataand client using the data to perform routing, e.g., shortest-path firstdecisions) are done on the STEP routers and not on the STEP server.However, in certain alternative embodiments, the STEP repository/servercan be configured to make or contribute to routing decisions.

The path tree database is used to store all data in the STEP repository.As the name suggests, each data set gets its own path in the path treedatabase. The following path definition format will be used to publishSTEP related information from each STEP router in an exemplaryembodiment:

-   -   /<authority-name>/<district-name>/<router-name>/step=<router        document> where,        -   authority-name: Name of the authority to which the router            belongs        -   district-name: Name of the district to which this router            belongs.        -   router-name: Name of the router        -   step: leaf of the path where the j son document is stored

Districts are explained in detail in the following sections. For now, adistrict can be considered as a collection of neighborhoods and a way ofsegmenting routers within an authority.

Each STEP router publishes a set of router documents to the STEPrepository. A STEP router can be a member of one or more districts, andeach STEP router publishes one router document for each district ofwhich it is a member. Each STEP router generally subscribes to the STEPdocuments of all other STEP routers within each district of which it isa member. In this way, each STEP router learns the service availabilityacross each district of which it is a member and can apply algorithms ona per-service basis to determine the available paths for a service inthe network. Each STEP router runs routing (e.g., SPF) calculationsperiodically and does not receive any end notifications from the server.

In an exemplary embodiment, the following types of information will bestored in the STEP repository:

-   -   Service availability within each router    -   Peer paths available from each router    -   External routes learned from other routing protocols if        distributed into STEP

Each of these types of information are discussed in greater detailbelow.

The STEP repository provides a complete view of network serviceavailability at any given time and also can maintain a history of thechanges that happened in the network over a period of time. Among otherthings, this current and historical information can be used fordebugging or fine-tuning service policies, e.g., to prioritize variousservices at different times of the day, and also can be used toeffectively revert to prior network states if necessary or desirable.Other machine learning algorithms can also be applied to the dataobtained from STEP repository to help influence the services in thenetwork.

Path Tree Server as Step Repository

The path tree database is a lightweight, scalable, in-memorysubscription datastore. It supports a socket-based publisher-subscribermodel. The data set is stored as various paths, and clients can addwatches on various paths to be notified of changes. An example isprovided below.

-   -   /p1/p2/p3/key=“test”    -   where,    -   /p1/p2/p3/key is the path    -   test is the value.

STEP clients can create paths and also can subscribe for notificationson any path. For example, a client can add a watch on the path/p1/p2 andit will get notification when anything gets created/changed/removedunder the/p1/p2 path.

Path tree clients store the data-set as JSON (although any data encodingcan be used). Any further updates to the data-set will be sent as JSONpatch documents (JSON diffs) as specified in IETF RFC 6902 entitledJavaScript Object Notation (JSON) Patch and available athttps://tools.ietf.org/html/rfc6902, which is hereby incorporated hereinby reference in its entirety. This provides an efficient way to updatethe states as well as notify watchers of the updates instead of sendingthe whole JSON file. This mechanism should work particularly well forrouting change notifications where only a few routes maybe be advertisedor withdrawn based on routing changes. So only those changenotifications will be sent by the path tree clients.

The STEP server notifies all subscribers of any changes to the paths towhich they have subscribed. The server preferably also keeps a historyof all JSON diff updates to a particular path. These updates areconsidered as network path changes or route changes. Periodically, thesediffs will be combined into one JSON document (by default, this isconfigured to be 100 diffs per path) to allow for rollover andaggregation.

The path tree server is stateless and is not a persistent datastore. Ifrestarted, it loses all state information, and clients must re-populatethe datastore with the latest states, i.e., the latest STEP documents.

In order to persist the states in the path tree server, a separate pathtree client will listen to all paths on the server and store it in atime series database. This path tree client can either co-reside withthe path tree server or it could be remote. This time series databasecan be used by analytics/web client to determine the network changesover time. This is discussed in greater detail below.

Step Repository/Server Location

The STEP repository and STEP server can be hosted virtually anywhere,although in practice they will reside in one of the following threelocations:

Conductor

STEP server can be co-located on the Conductor. The Conductor isaccessible by all routers, which is how the routers are initialized andbootstrapped. Thus, generally speaking, the Conductor would be thenatural (e.g., default) location for the STEP repository. If Conductoraccess from the routers is on a “lossy” network or has high latency, theSTEP repository should be hosted on a server that is close to therouters or on the routers themselves.

A Common Server Accessible by all Routers

The STEP server can be located on a standalone server, separate from theConductor. This generally would require implementation of secure accessfrom all routers.

Routers Themselves (e.g., Data Centers)

There are several deployments where the connectivity to the Conductor isunreliable and may not be available for extended periods of time suchthat the routers would not be able to talk to each other. In thesecases, route exchanges and forwarding should still be able to functionwithout disruption. In order to achieve this, the STEP repository canreside on a router (generally a hub router) that can be accessed by allrouters in that domain. It should be noted that a STEP router that hostsa STEP repository effectively acts as both a STEP server (for managingthe STEP repository) and a STEP client (for transmitting service andtopology state information to the STEP repository/server and forreceiving service and topology state information from the STEPrepository/server).

Step Server and Client Devices

As discussed above, the STEP repository and STEP server can beimplemented in any of various types of devices such as, for example, aSTEP router, the Conductor, or a server that is separate from the STEProuters and the Conductor. FIG. 1 is a schematic diagram showing majorcomponents of the STEP server 100, in accordance with one exemplaryembodiment. Among other things, the STEP server 100 includes a datastore110 and a STEP server controller 120. The datastore 110 includes avolatile memory in which the route repository is stored (referred tohere as the Volatile Route Repository 111) and a persistent storage inwhich historical STEP information is stored (referred to here asPersistent Historical Information 112). The STEP server controller 120typically includes a microcontroller and related peripherals withsoftware that is stored in a tangible, non-transitory computer-readablemedium and that is run on the microprocessor to implement one or morecomputer processes that perform STEP server functions described herein.When the STEP server 100 is implemented in a STEP router, themicrocontroller on which the STEP server controller 120 is implementedmay be the same microcontroller that runs other router functions such ascomputation of routes and routing of packets.

FIG. 2 is a logic flow diagram for the STEP server controller 120 inimplementing the high-level STEP server functions, in accordance withone exemplary embodiment. In block 202, the STEP server controller 120maintains the STEP repository in the datastore. In block 204, the STEPserver controller 120 receives service and topology state informationfrom each of a plurality of STEP routers using the service and topologyexchange protocol. In block 206, the STEP server controller 120 storesthe received service and topology state information in the STEPrepository. In block 208, the STEP server controller 120 transmits, toeach router, using the service and topology exchange protocol, serviceand topology state information from the STEP repository for at least oneother router based on configured relationships between routers to enableeach STEP router to make routing decisions based at least in part on theservice and topology state information from the at least one otherrouter.

As discussed above, the STEP client is implemented in the STEP router.FIG. 3 is a schematic diagram showing major components of the STEPclient 300, in accordance with one exemplary embodiment. Among otherthings, the STEP client 300 includes a datastore 310 and a STEP clientcontroller 320. The STEP client controller 320 maintains in thedatastore 310 a local STEP repository 311 that is used to store STEPdocuments received from the STEP server. The STEP client controller 320typically includes a microcontroller and related peripherals withsoftware that is stored in a tangible, non-transitory computer-readablemedium and that is run on the microprocessor to implement one or morecomputer processes that perform STEP client functions described herein.The microcontroller on which the STEP client controller 320 isimplemented may be the same microcontroller that runs other routerfunctions such as computation of routes and routing of packets. WithSTEP, the router generally also includes a STEP-enhanced routing engine340 that uses the STEP information in the local STEP repository 311along with traditional routing information 313 stored in the datastore310 (e.g., static routes, connected routes, and/or routes from a routingprotocol such as OSPF or BGP) to determine routes for the routinginformation base 314 upon which the STEP-enhanced routing engine 340routes packets.

FIG. 4 is a logic flow diagram for the STEP client controller 220 inimplementing the high-level STEP client functions, in accordance withone exemplary embodiment. In block 402, the STEP client controller 220transmits service and topology state information to the STEP serverusing the service and topology exchange protocol. In block 404, the STEPclient controller 220 receives, from the STEP server, using the serviceand topology exchange protocol, service and topology state informationfor at least one other router based on configured relationships betweenrouters. In block 406, the STEP client controller 220 stores thereceived service and topology state information

for the at least one other router in a local STEP repository for use inmaking routing decisions.

As discussed above, both the STEP server 100 and the STEP client 300 canbe implemented in a router.

Step Repository Redundancy

In an exemplary embodiment, the path tree server is a non-persistentdatastore. Path tree servers can be deployed with multiple instances toincrease resilience. In the event there are multiple path tree servers,one of the servers will be elected as primary and the rest of theservers will be secondary servers. In exemplary embodiments, thiselection may be based on the lowest boot up timestamp or based on thehighest configured priority, although other election schemes may beemployed. Clients that connect to a secondary server will have theirrequests proxied to the primary server. Secondary server repositorieswill not maintain any path tree state within them.

In the event a primary server fails or reboots, one of the secondaryservers will assume the role of the primary based on the election scheme(e.g., based on the next—lowest boot up timestamp or based onnext-highest configured priority). Any requests to the old primary(which is now a secondary) will be relayed to the new primary. If thepriority is configured, then once the failed primary with highestpriority comes back up, it will assume leadership again. The new primaryneeds to be repopulated by all routers, as it saves no state.

All STEP servers (primary and secondaries) should be able to communicatewith each other over a L2 or L3 network. The STEP servers can beconfigured with priorities. In an exemplary embodiment, the highestpriority server will be the primary and the remaining servers will besecondary servers. The STEP primary can be configured taking intoconsideration the reachability constraints in the network. The nextsection describes the various locations where STEP server can reside.

Step Repository Configuration

The STEP repository location(s) and optional priority settings can beconfigured by the network administrator based on the needs of thenetwork deployment. The data model changes for the STEP repository isgiven below.

grouping step-repo {  leaf description {   type string;   description   “A description about the STEP repository.”;    t128ext:example “STEPrepository on conductor”;  }  leaf address {   typet128ext:hostv4-prefix;   description    “Address of the STEP server.This could be the IP address/FQDN of the Conductor, standalone server orrouter where the STEP server is hosted.”;  }  leaf priority {   typeuint8;   default 0;   description    “The priority assigned to the STEPserver. The STEP server with the highest priority will become primary.If no priority is assigned to any servers, the server with the longestuptime will be the primary.”;  } container authority {  ...  leaf-liststep-repos {   description “Location of the STEP repository”;   usesstep-repo;  }  ... }

The STEP server can be setup by configuring the following twoparameters:

IP Address/FQDN

The STEP server can be identified using an IP address or Fully QualifiedDomain Name (FQDN). The STEP server can be the Conductor, a standaloneserver, or a router itself. If this field matches the IPaddress/hostname of an interface on a router, then the STEP server willbe setup on that router. A STEP service will be generated for each ofthese IP addresses with the corresponding service routes for each routerso that the STEP clients on the routers can reach the STEP repository.This will be done by the config generator before the config is pusheddown to all routers. More details are provided below.

Priority

This is an optional parameter which would be very useful in some networkdeployments. Priority indicates which server should be the primaryserver in the event there are multiple servers. By default, the serverthat has the longest uptime becomes the primary. However, with priorityconfigured, the server with the highest priority will instead become theprimary. Upon failure to become the primary, the next highest prioritywill become primary, and so on. If more than two STEP servers aredeployed and some have priority configured and some do not, the one withthe highest priority that is active will become primary. When allservers with priority configured are unavailable, uptime is used as adiscriminator for the remaining servers. This becomes useful indeployments to specify primary servers on nodes which are reachable byall network elements. This could be even a router (e.g., in the eventconductor or standalone server has lossy connections).

Step Document

In an exemplary embodiment, the STEP document is a JSON documentpublished by each STEP router to the STEP repository. The protobufdefinitions below illustrates the different fields that make up theJSON.

syntax = “proto3”; message IpPrefix {  /* IP Address */  stringipAddress = 1;  /* Prefix length */  int32 prefixLength = 2; } messageServicePolicy {  /* Name of the service policy */  string name = 1;  /*Indicates the path has acceptable SLA  bool hasSla = 2; } messageSlaValues {  /* Latency in milliseconds */  uint32 latency = 1;  /* Lossin percentage */  double loss = 2;  /* Jitter in milliseconds */  uint32jitter = 3; } message PeerPath {  /* Unique name identifying the path toa target 128T peer */  string identifier = 1;  /* Local interfacehostname */  string hostname = 2;  /* Local interface IP address */ string ipAddress = 3;  /* Target peer name */  string peerName = 4;  /*Vectors associated with the path */  repeated string vector = 5;  /* SLAvalues */  SlaValues slaValues= 6;  /* List of service policies */ repeated servicePolicy = 7; } enum RouteSourceType {  District = 0; Authority = 1; } message RouteSourcePath {  /* Source type */ RouteSourceType source Type = 1;  /* Name of the source */  string name= 2; } message ServiceNexthop {  /* Vectors associated with the nexthops*/  repeated string vector = 1;  /* District or authority list */ repeated RouteSourcePath sourcePath = 2; } message RouteNexthop {  /*Routing cost associated with the nexthops */  repeated int32 cost = 1; /* District or authority list */  repeated RouteSourcePath sourcePath;} message ServiceRoute {  /* Name of the configured service-route */ string name = 1;  /* List of nexthops */  repeated ServiceNexthopnexthop = 2; } message Route {  /* Ip prefix associated with the service*/  IpPrefix ip_prefix = 1;  /* Next hop associated with the route */ repeated RouteNexthop routeNexthop = 2; } message ActivePeerPath {  /*Unique name identifying the active path to a target 128T peer */  stringidentifier = 1; } message Service {  /* Service name */  string name =1;  /* Routes associated with the service */  repeated Routes routes =2;  /* Configured service-routes */  repeated ServiceRoute serviceRoutes= 3; } enum Protocol {  Connected = 0;  BGP  = 1;  OSPF  = 2;  Static =3; } message ExternalRoute {  /* Protocol that distributed the externalroute */  Protocol protocol = 1;  /* External routes distributed intostep */  repeated Route route = 2; } message Node {  /* Name of the node*/  string name = 1;  /* Services */  repeated Service service = 2;  /*Paths between peering routers */  repeated PeerPath peerPath = 3;  /*External routes distributed into Step */  repeated ExternalRouteexternalRoute = 4;  /* InterConnect denoting the path between nodes */ Repeated string interconnect = 5; } message Router {  /* Name of therouter */  string name = 1;  /* Nodes in a router */  Repeated Nodenodes = 2; }

The protobuf definitions above provide a scheme for third-party routersto interact with STEP routers by publishing their router documents asJSON documents. Protobufs have accessors to get/set values and they canbe converted to and from JSON. The following is an example JSONrepresentation of the document:

{  name : ″EastRouter″  nodes : [ {   name : ″node1″,   peerPaths : [   {     identifier : ″peer1+3.5.6.7+node1+intf1+vlan0″,     hostname :″EastRouter.nodel.intf″,     peerName : ″peer1″,     vector : [″broadband″, ″mpls″ ],     service-policy : [ {      name : ″test″,     hasSla : true     } ],    },    {     identifier :″peer1+4.5.6.7+node1+inft11+vlan0″,     ipAddress : ″10.2.3.4″,    peerName : ″peer1″,     vector : [″lte″],     slaValues : {     loss : 10,      latency : 30,      Jitter : 10     },    service-policy : [ {      name : ″test″,      hasSla : false     } ]   }   ],   service : [ {    name : ″database″,    route : [ {    ipPrefix : ″1.2.3.4″,     prefixLength : 32,     nexthop : [ { cost: 10 } ]    },    ipPrefix : “2.5.6.0”,    prefixLength : 24   service-route : [ {     name : ″service-route1″,     serviceNexthop :[ {      vector : [ {″red″, “blue” } ]     } ],    } ]   } ],  external-routes : [ {    route : [ {     ipPrefix : ″192.168.3.0″,    prefixLength : 24,     nexthop : [ { cost : 10 } ],    } ],   protocol : ″bgp″   } ],   interconnect : [ { ″fabric1″} ]  },  {  name : ″node2″,   peerPaths : [    {     identifier :″peer2+3.5.6.7+node2+12+0″,     hostname : ″EastRouter.node2.intf″,    peerName : ″peer2″,     vector : [″mpls″],     slaValues : {     loss : 20,      latency : 10,      jitter : 0     },    service-policy : [ {      name : ″test″,      hasSla : false     } ]   }   ],   service : [ {    name : ″database″,    route : [ {    ipPrefix : ″2.5.6.0″,     prefixLength : 24    } ],    service-route: [ {     name : ″service-route2″,     serviceNexthop : [ {      vector: [ {″red″} ]     } ]    } ]   } ]  } ] }

The STEP document has the following fields, which will be populated byeach network element.

1. Router

Router is the top-level entity, which encompasses one or more nodes.Each STEP document belongs to a router. A router can have one or morenodes connected via an interconnect (backplane).

2. Node

Each node lists the services, peer-paths reachable from the node,service availability, external routes distributed by other protocols,and the interconnects available between multiple nodes. The presence ofinterconnects will be used to determine reachability of service routesbetween the nodes. If the interconnect is absent from the document, thisindicates that the path between the nodes are down and some serviceshosted by the other node(s) will not be accessible via “this” node. Anypeer paths via the node that is down (absent from the document) will notbe considered for service reachability.

3. Services

The Services section denotes all services that are being advertised byeach router. A router advertises services if a route matches theconfigured service prefix or if there is a configured service route. Inshort, a service entry for a router essentially means that the routercan provide that service.

Services are advertised with prefixes and nexthops. If the prefixes havenexthops associated with them, it means that the routes are learned fromrouting protocols and the nexthops are from routing. The prefixes withina service may be withdrawn if the route that contributes to this prefixgets withdrawn. The narrower of the configured service prefixes getsadvertised. For example: if the service is configured with a prefix of10.10.10.0/24 and the route that gets applied is 10.10.10.1/32, then theservice will be advertised using the 10.10.10.1/32 prefix, as it isnarrower. The prefixes from a routing protocol get applied to a serviceonly if it is distributed into STEP. More details about this aredescribed below.

Services can also have prefixes without nexthops. These are prefixesobtained directly from the service address configuration, for whichthere are configured service routes. Service routes can be consideredsimilar to static routes in that they are explicitly configured but areservice-specific.

The Service route section indicates the configured local nexthopsavailable. This section will only advertise the nexthops that arereachable. If the next hops are down, the service route section will beempty.

4. Peer Path

Peer paths indicate all paths available from a given router to each ofthe peers. This information can be used to build the graph representingthe network topology connections between routers.

Since SSR routing is service oriented, the peer paths themselves do notgive a complete picture of the service availability. Each service has aservice policy associated with it, and each of the peer paths should bewithin the acceptable SLA. Every peer path has a list of servicepolicies associated with it and indicates whether it is withinacceptable SLA for each policy. Each service can therefore use thisservice policy information to determine if these paths are usable for aparticular service. In an exemplary embodiment, the service policy forSLA values includes a configurable hold down timer, and the path mustremain within SLA during this timer before being advertised as withinacceptable limits to the STEP server. It is the responsibility of therouter (STEP client) to honor the hold down timer and SLA thresholds forthe generation of its STEP document.

SLA values are also advertised per peer path. In an exemplaryembodiment, there is a configurable timer value per adjacency that canbe setup to update these values periodically. SLA incorporates loss,latency and jitter values of the path. These typically are measuredevery few seconds on the routers themselves, but will not be updated inthe STEP repository that frequently in order to avoid flaps (e.g., asituation in which a router alternately advertises a destination via oneroute then another or as unavailable and then available again in quicksequence, or alternatively advertises an interface as down and then upin quick succession) and to avoid frequent routing updates that canprevent network convergence. These values may be updated, for example,every 5 minutes (as a rolling average), which can be overridden. Thesevalues, if advertised, will be incorporated into the routing (e.g., SPF)calculation to determine the best path based on SLA.

5. External Routes

External routes refer to the routes that are distributed into STEP fromsome other routing protocols (e.g., BGP routes redistributed into STEP).This is a case where the routing protocol is not advertised into anyservices, just into STEP, so that all other routers can learn thisroute. These can be redistributed back into the BGP at another STEProuter.

Neighborhoods

A neighborhood is a label applied to a network interface to indicatenetwork connectivity. When two network interfaces share the sameneighborhood, it implies that they have network reachability.Neighborhoods can be published by each router as part of the STEPdocument, including its vector, the network interface, and tenancyinformation. This can be used to determine peer path connectivitybetween routers. An example configuration is given below.

network-interface {  name test-interface  vlan 0  neighborhood test  ...}

In an exemplary embodiment, neighborhoods from all router configurationsare read by the Conductor, and adjacency configuration is generated bythe config generation code. The adjacency configurations on each routerserve as the available peer paths. These peer paths will be advertisedas part of the STEP document. This will allow each peer to create atopology graph of the whole network on a per service basis.

Districts

A district is a logical grouping of neighborhoods. STEP documentsgenerally are shared between all routers within the same district. Thereis no strict demarcation for districts and it instead depends entirelyon how the network topology is segmented. This section provides examplesof how the same network topology can be segmented as one district ormultiple districts.

Single District

FIG. 5 is a schematic diagram showing an exemplary topology segmented asone district with multiple neighborhoods. In this example, the districtname is “common” and there is a hub and spoke topology. Routers DC1 andDC2 are the hubs. Routers Br1 and Br2 are spokes connected to routerDC1. Routers Br3 and Br4 are spokes connected to router DC2. Thefollowing neighborhoods are defined:

-   -   1. N1        -   All WAN interfaces of DC1, Br1 and BR2 are in neighborhood            N1. This neighborhood is part of district “common.”    -   2. N2        -   All WAN interfaces of DC2, Br3 and BR4 are in neighborhood            N2. This neighborhood is also part of district “common.”    -   3. N3        -   The WAN interface reachable between DC1 and DC2 are in            neighborhood N3. This neighborhood is also part of district            “common.”

In this example, all three neighborhoods have been defined as part ofthe same district “common.” This means that all six routers will publishtheir STEP documents into the same path of the STEP server. Thefollowing shows an example path where the documents are published:

<authority-name> : auth128 /auth128/common/DC1/step=<json>/auth128/common/DC2/step=<json> /auth128/common/Br1/step=<json>/auth128/common/Br2/step=<json> /auth128/common/Br3/step=<json>/auth128/common/Br4/step=<json>

Multiple Districts

FIG. 6 is a schematic diagram showing the same topology as FIG. 5 butsegmented into multiple districts. In this example, there are threedistricts, specifically a district named “east” including routers DC1,Br1, and Br2; a district named “west” including routers DC2, Br3, andBr4; and a district named “central” including routers DC1 and DC2. EachSTEP router publishes its STEP documents in its respective paths. Thefollowing shows example paths for the districts shown in FIG. 6 :

<authority-name> : auth128 District east /auth128/east/DC1/step=<json>/auth128/east/Br1/step=<json> /auth128/east/Br2/step=<json> Districtwest /auth128/west/DC2/step=<json> /auth128/west/Br3/step=<json>/auth128/west/Br4/step=<json> District central/auth128/central/DC1/step=<json> /auth128/central/DC2/step=<json>

It can be seen that router DC1 published its STEP document in twodistricts, east and central, and router DC2 also published its STEPdocument in two districts, west and central. Routers Br1 and Br2 onlypeer with router DC1 in the east district, so routers Br1 and Br2 onlypublished their STEP documents in the east district because theirnetwork topology and service availability, on a per branch basis, neednot be exposed to the other districts. Similarly, routers Br3 and Br4only peer with router DC2 in the west district, so routers Br3 and Br4only published their STEP documents in the west district because theirnetwork topology and service availability, on a per branch basis, neednot be exposed to the other districts. If all the branches wereconnected as a full mesh, then each branch router would need to know theservice availability and reachability to every other branch, but that isnot the case here. In this example, router DC1 can effectively hide allof its branches from router DC2, and vice versa.

In an exemplary embodiment, each router that is part of multipledistricts will aggregate the service and route information from onedistrict and advertise that to another district. Hence, the STEPdocument for the same router on two different districts will lookdifferent. Additional details on how the services are exchanged betweendistricts are provided below.

District Configuration

Below are the data model changes needed to configure a district, inaccordance with one exemplary embodiment. District is a container at theauthority level containing a list of neighborhoods. Each neighborhoodcan have a list of districts associated with it.

container authority {  ...  list district {   key ″name″;   ordered-byuser;   Description ″Districts in the authority.”;   leaf name {    typet128ext:district-id;    description     ″Name of the district.″;   }  leaf-list neighborhood {    type t128ext:neighborhood-id;   description     ″Neighborhoods which belong to this district″;   }  }}

Default District

In an exemplary embodiment, associating a neighborhood to a district isoptional. When a neighborhood is not associated explicitly with adistrict, it will be assigned the district “default-district”. This way,it is not mandatory to configure districts if the topology only demandsa single district. In the topology described with reference to FIG.above, if all neighborhoods were configured without districts ratherthan with district “common,” then the pathTree server would have thefollowing paths.

<authority-name> : auth128 /auth128/default-district/DC1/step=<json>/auth128/default-district/DC2/step=<json>/auth128/default-district/Br1/step=<json>/auth128/default-district/Br2/step=<json>/auth128/default-district/Br3/step=<json>/auth128/default-district/Br4/step=<json>

The following rules are used when configuring neighborhoods anddistricts in one exemplary embodiment:

-   -   If a router R1 has an interface with neighborhood N1 in district        D1 and another interface with no neighborhood configured, R1        will publish the router document under district D1 only. It will        not publish a document under “default-district.”    -   If a router R1 has an interface with neighborhood N1 in district        D1 and another interface in another neighborhood N2 which is not        part of any districts, R1 will publish STEP documents under D1        and “default-district.”    -   If router R1 has no neighborhoods configured on any of its        interfaces, it will not publish any STEP document.

Routing Calculations Using Step

The routing (e.g., SPF) calculation runs on demand on a router using ahold down timer, e.g., if there are any updates from the STEP repository(including local changes), it will be scheduled to recalculate the pathsafter a predetermined amount of time, e.g., five seconds. This generatesservice-based routes and nexthops. These will be pushed down to therouting agent to setup Forwarding Information Base (FIB) entries. Thefiring of the timer indicates that it is time to compute paths, andthere is no end notification from the server.

Once a router reads all the STEP documents, it will run its routingalgorithm (e.g., SPF via Dijkstra's algorithm) across all availablepaths advertised by other routers on a per service basis. In some cases,this will be run on a per service prefix if each of the service prefixeshas a different nexthop (this could be the case for prefixes distributedinto a service from other protocols).

The cost of each path is published in the STEP document and the servicepolicy associated with each service can be obtained from config. Basedon this, the logical network topology is different per service. The SPFcalculates a best path and an alternate loop free path for each service.The alternate path will be used as a backup in the event the primarypath is not available.

SLA values are advertised per peer path periodically. The time for theseupdates can be configured per adjacency. Each peer path advertised alsoindicates if the SLA per service policy is being met. Service policywill have a path hold down timer field which can be configured tocontrol these updates. The following are example data model changes forpath SLA update:

Data model changes for path SLA update list network-interface {  ... list adjacency {   leaf sla-update-timer {    type uint64;    unitsseconds;    default “300”;    Description “Periodic time for updatingper path SLA.”;   }  }  ... } Data model changes for SLA hold down timerlist service-policy {  ...  leaf sla-hold-down-timer {   type uint64;  units seconds;   default “60”;   description    “Hold down time forSLA to be within acceptable limits before declaring the path as up”;  } ... }

Service Exchange

In an exemplary embodiment, the following types of services areavailable on a router:

-   -   a) Services with authority wide scope.    -   b) Local Services that are local to the router or shared between        N routers.    -   c) Hosted services that are for services hosted by the router        for local access.    -   d) Application Identification services that are local to the        router.

Of these service types, STEP only advertises the following services inthe STEP document in an exemplary embodiment:

-   -   a) Services with authority wide scope.    -   b) Local Services that are shared between more than one router.        If the service is local to that router, then it will not be        advertised.

The other two types of services are only relevant locally to the routerand therefore will not be published in the STEP document in an exemplaryembodiment.

FIG. 7 is a schematic diagram showing a topology including two routerspeering with each other. In this example, router R2 has a service-routefor service S1 and there are two peer paths between routers R1 and R2.Consider, for example, that service S1 is configured with prefix1.2.3.0/24 and with service-route on router R2.

Router R1

-   -   Obtains service S1 via configuration    -   Has no routes that match the service prefix S1    -   Has two peer paths

Router R1 does not have any services to advertise, as it has no routesmatching that service nor any service nexthop configured. Thus, thefollowing is an example STEP document for router R1:

{  node : [ {   name : “node2”,   peerPaths : [    {     identifier :“peer2+3.5.6.7+node2+dev1+intf1”,     hostname : “R2.node2.intf1”,    peerName : “peer2”,     vector : [ “mpls” ]    },    {    identifier : “peer2+3.5.6.7+node2+dev2+intf2”,     hostname :“R2.node2.intf2”,     peerName : “peer2”,     vector : [ “broadband” ]   }   ]  } ] }

From the STEP document above, router R1 does not advertise any services.It does, however, have peer paths to the east router, R2.

Router R2

-   -   Obtains service S1 via configuration    -   Has no routes that match the service prefix S1    -   Learns about a local service-route on the node N1 via        configuration.    -   Has two peer paths

The following is an example STEP document for router R2:

{  node : [ {   name : “node2”,   peerPaths : [    {     identifier :“peer2+3.5.6.7+node2+dev1+intf1”,     hostname : “R1.node2.intf1”,    peerName : “peer2”,     vector : [ “mpls” ]    },    {    identifier : “peer2+3.5.6.7+node2+dev2+intf2”,     hostname :“R1.node2.intf2”,     peerName : “peer2”,     vector : [ “broadband” ]   }   ]   service : [ {    name : “S1”,    route : [ {     ipPrefix :“1.2.3.0”,     prefixLength : 24    } ],    service-route : [ {     name: “service-route1”,     serviceNexthop : [      { vector : “red” }    ],    } ]   } ]  } ] }

For router R2, service S1 is advertised as part of the STEP documentwith a service-route. This simply means that service S1 is available onrouter R2. When router R1 receives the STEP document of router R2, itdiscovers that the service S1 is available on router R2, and since thepeer path is above the SLA, it would set up a service topology forservice S1 from router R1 to router R2. When router R2 receives the STEPdocument from router R1, it finds no services are being advertised.Hence, the only nexthop for service S1 will be the configured serviceroute on router R2. The above example indicates how the services areexchanged among multiple routers within the same district.

Removal of a Router

A router may be become unavailable for any of a variety of reasons, suchas, for example, a failure of the router, unavailable or poorcommunication connectivity to the router, a shutdown of the router by anetwork administrator, or removal of the router from the networkconfiguration (e.g., through a notification to the STEP server). Suchunavailability can be conveyed to the STEP repository and, from there,propagated to other routers that subscribe to updates for thenow-unavailable router. For example, if the router fails or is shutdown, or if communication to the router is interrupted, the router maystop communicating with the STEP server/repository, in which case theSTEP server may (possibly after trying a predetermined number of timesto re-establish communication with the server) update the STEPrepository to indicate that the router is unavailable, e.g., by removingthat router's state information from the STEP repository or by updatingthat router's state information to indicate unavailability. Similarly,if the router is removed from the network configuration, the STEP servermay update the STEP repository to indicate that the router isunavailable, e.g., by removing that router's state information from theSTEP repository or by updating that router's state information toindicate unavailability. In any case, the STEP server may immediatelynotify other routers that subscribe to updates for the now-unavailablerouter that the router is now unavailable, in which case these otherrouters may re-calculate one or more routes to avoid the now-unavailablerouter.

Redistributing Protocols into Step

STEP routers often need to interact with other routing protocols likeBGP, OSPF etc., in order to learn routes. Instead of running theseprotocols in the core, STEP routers have the unique ability todistribute these routes selectively into STEP. In one specific exemplaryembodiment, the following routing protocols can be distributed intoSTEP:

-   -   a) BGP    -   b) OSPF    -   c) Static    -   d) Connected

The following is an exemplary configuration for distributing routingprotocols into STEP:

grouping redistribution {  typedef redistribute-into-step {   typeenumeration    enum connected {     description “Interface routes”;    }   enum bgp{     description “BGP routes”;    }    enum static {    description “Static routes”;    }    enum ospf {     description“OSPF routes”;    }   }  }  list redistribute {   key protocol;  description    “List of routing protocols to redistribute into STEP”;  leaf protocol {    description     “The routing protocol toredistribute into STEP”;    type redistribute-into-step;   }   leaf-listservice {    description     “List of services to which the routes areapplied.”;    type auth:service-ref;   }  }  augment“/t128:config/authy:authority/authy:router/rt:routing” {  list step {  key name;   description “STEP instance configuration”;   max-elements1;   leaf name {    type string    description “STEP instance name”;   }  uses redistribution;  } }

This can be extended in the future to apply filter policies oncommunities, peer group, etc., to filter routes at a more granularlevel. In an exemplary embodiments, there are two ways these routes canbe redistributed into STEP:

-   -   a) Redistribute into selected services    -   b) Redistribute as external routes

Redistribute Protocols into Services

FIG. 8 is a schematic diagram showing an example of redistributing BGPinto services. In this example, router R1 is peered with router R2, androuter R2 is BGP peering with a non-STEP router (R3). Consider thefollowing exemplary configuration on router R2 where BGP isredistributed into service S1 via STEP:

Step  name : “step1”  redistribute   protocol : bgp  service : [ { “S1”} ]

Now, consider the same service S1 as in the previous example with thesame prefix 1.2.3.0/24. In this case, S1 has no service routesconfigured. The idea is to learn routes from BGP and redistribute theminto service S1. For this example, it is assumed that only one route islearned via BGP, specifically route 1.2.3.4/32.

Router R1

-   -   Obtains service S1 via configuration    -   Has no routes that match the service prefix S1    -   Has two peer paths

Router R1 does not have any services to advertise, as it has no routesmatching that service nor any service next-hop configured. The followingis an example STEP document for router R1:

{  node : [ {   name : “node2”,   peerPaths : [ {    identifier :“peer2+3.5.6.7+node2+12+0”,    hostname : “R2.node2.intf”,    peerName :“peer2”,    vector : [ “mpls” ]   } ]  } ] }

From the STEP document above, it is clear that router R1 is notadvertising any services. It has peer paths to the east router.

Router R2

-   -   Obtains service S1 via configuration    -   Has BGP routes that match the service prefix S1. The narrower        prefix is advertised.    -   Has two peer paths

The following is an example STEP document for router R2:

{  node : [ {   name : “node2”,   peerPaths : [ {    identifier :“R1+3.5.6.7+node2+12+0”,    hostname : “EastRouter.node2.intf”   peerName : “peer2”,    vector : [ “mpls” ]   } ],   service : [ {   name : “S1”,    route : [ {     ipPrefix : “1.2.3.4”,    prefixLength : 32,     nexthop : [ { cost : 10 } ]    } ]   } ]  } ]}

The nexthop is provided as cost. Since legacy routing protocols are notaware of vectors, the cost of the route is used directly. This cost willbe used when calculating the best path along with the vector magnitudeson each path. In an exemplary embodiment, AS path length will beconverted into a cost by multiplying the number of ASs in the path witha constant (e.g., 10) and the cost will be advertised in the nexthop.The AS-path also could be advertised in the document to propagate it inthe future for transit cases.

For router R2, service S1 is advertised as part of the STEP documentwith a narrower prefix and with a nexthop. This means that service S1 isavailable on router R2. Router R2 published service S1 as part of itsrouter document because:

-   -   BGP was redistributed into the service S1 in router R2    -   The route learned from BGP was a subset of the service prefix

The same can be done for other protocols listed in the enumeration,namely static, connected and OSPF.

Redistributing Protocols as External Routes

With this option, the routes learned from BGP will be distributed intoSTEP as external routes. One use case where this option is useful is toadvertise the connected routes of peer routers into BGP where theseserve as reverse routes for downstream non-SSRs. However, this is notconsidered a normal mode of operation and should be the least preferredway of advertising routes, as STEP is not considered as a protocol tocarry legacy routes across the network.

FIG. 9 is a schematic diagram showing an example of redistributing BGPinto STEP. In this example, router R2 learns routes via BGP by peeringwith another router R3. In this case, router R2 is configured todistribute BGP into STEP. In this example, these routes are notdistributed into services. This is an important distinction from theprevious example, where the routes were distributed into services.Consider this configuration on router R2 where BGP is redistributed intoSTEP:

Step  name : “step1”  redistribute   protocol : bgp

In this case, the routes show up the in external route section of theSTEP document of router R2. It should be noted that router R2 does notadvertise the service S1 any more, as there are no routes that match theservice.

Router R2

-   -   Obtains service S1 via configuration    -   Has no routes that match the service prefix S1 as BGP is not        distributed into S1 service    -   Has external routes as BGP is distributed into STEP    -   Has two peer paths

The following is an example STEP document for router R2:

{  node : [ {   name : “node2”,   peerPaths : [ {    identifier :“R1+3.5.6.7+node2+12+0”,    hostname : “EastRouter.node2.intf”,   peerName : “peer2”,    vector : [ “mpls” ]   } ]   external-routes :[ {    route : {     ipPrefix : “1.2.3.4”,     prefixLength : 32,    nexthop : [ { cost : 10 } ]    },    protocol : “bgp”   } ]  } ] }

The protocol section in the external-routes section indicates whichprotocol was distributed into STEP. This document indicates that route1.2.3.4/32 from BGP was distributed into STEP. This does not mean thatthis route was distributed back to another protocol on router R1. Thepresence of this route does not affect any services, as it will NOT beapplied on any services. In certain exemplary embodiments, the only waythese routes can be used is if one of the peering routers distributethese external routes back into BGP. Additional details of this areprovided below.

Redistributing Step into BGP

Each router can learn services and routes from the STEP repository andredistribute them back into BGP. The redistribution can be more granularat the service level, where a set of services can be redistributed. Someexemplary data model changes for this are shown below, highlighted inbold.

This extension to the existing configuration provides a list of servicesthat can be distributed into BGP. By default, with the serviceenumeration, all services will be redistributed into BGP.

New enum in BGP redistribution grouping redistribution {  typedefredistribute-into-bgp {   type enumeration {    enum connected {    description “Interface routes”;    }    enum service {    description “Service routes”;    }    enum static {     description“Static routes”;    }    enum ospf {     description “OSPF routes”;    }   enum step {     description “Routes learned through STEP”;    }   } } Augment BGP routing policy config. module routing-policy-config {namespace “http://128technology.com/t128/config/routing-policy-config”;........  identity service-filter {   base filter-type;   Description“Filter based on services”;  }  identity service-filter-condition {  base condition-type;   Description “An service filter condition”;  } identity step-external-routes-condition {   base condition-type;  Description “STEP external routes condition”;  } ....... } augment“/t128:config/authy:authority” {  container routing {   description“authority level routing configuration”;   leaf service {    when“../../type = ‘rp:service-filter’”;    description “The serivce tomatch”;    type auth:service-ref;   }   must “../type !=‘rp:service-filter’ or service” {    error-message    “A service-filterrule must include a service.”;   }   ...  }  list policy {   key name”;  description    “A construct for processing which consists of a set of    statements executed in sequence”;   t128-codegen:base-object;   leafname {    description “A unique name used to identify the policy”;   type t128ext:name-id;   }   leaf service-filter {    when “../type =‘rp:service-filter-condition’”;    Description “The service filtername”;    type filter-ref;   }   must “type !=‘rp:service-filter-condition’ or ” +    “service-filter” {    error-message      “A service-filter-condition must include ” +     “a service-filter.”;    }   ...  } }

The “step” enumeration within protocol denotes all external routes thatwere learned via STEP. These are routes that do not match any servicesbut were distributed into STEP via other protocols (e.g. BGP, connected,static, etc.).

The “service” enumeration will distribute all services prefixes learnedfrom other routers into BGP if they are present in the router document,and will withdraw them if absent. The redistribute command has beenextended to provide a list of services that can be distributed into BGPin case not all service prefixes need to be exposed. This lets eachrouter have finer control over the services it chooses to advertise intoBGP.

Multicast Service

Multicast has many applications where a source needs to replicatepackets to one or more receivers. Currently, SSRs support unicastservices which are delivered to one destination. Unicast services do nottake into account multicast protocols like IGMP protocols, which areused to indicate which receivers are interested in a certain multicastgroup.

Access policy requirements for multicast services are also differentfrom that of unicast services. Unicast services generally have accesspolicies only for the source, whereas multicast services would benefitfrom access policies for the source as well as receiver on a per servicebasis.

A service with multicast IP address is a multicast service. A multicastservice will replicate packets to multiple endpoint destinations. Thedestinations can be local to the router or can be peer routers. Thefollowing is an example of a multicast service definition in accordancewith an exemplary embodiment:

Service  name : mcast,  id : 10,  address : 233.252.0.2/32,  scope :private,  access-policy : [   {    permission : “allow”,    source :“blue”   }  ],  multicast-sender-policy : [   {    permission : “allow”,   source : “red”   }  ]

Here, a multicast service named “mcast” is associated with a multicastaddress 233.252.0.2. It also has an access policy to allow a tenantnamed “blue” and a sender policy to allow a tenant named “red.” It isimportant to understand these terms, as they differ from the unicastworld.

The access-policy field indicates which receivers are allowed to acceptpackets from this multicast service. This is different from how unicastservices use access-policy. Unicast services use access policies for theoriginator of the packet (i.e. whether the source has access to thisservice). However, for multicast services, it is an access-policy forthe receivers.

The access-policy ensures that IGMP packets are received only from thereceiver tenants allowed on this service. A multicast address indicatesa multicast group. The multicast receivers can be can be dynamicallylearned via IGMP protocol.

In the example above, the access-policy allows receivers that areclassified as tenant blue. Here, the router would accept IGMP joins fromany interface that has tenant blue configured on it. IGMPv2 membershipquery messages for the 233.252.0.2 group are sent out of all interfacesthat have access to this multicast service. Any interface on the routerhaving a tenant that does not have access to the service will drop allIGMP membership report messages received for that multicast group. Thus,multicast services can impose access controls on the receivers.

The multicast-sender-policy indicates which sources are allowed to sendpackets to this multicast service. The following shows some exemplarydata model changes for the multicast-sender-policy:

service foo {  ...  list multicast-sender-policy {   key source;  description    “List of multicast sender policies by address prefix,QSN or    tenant and prefix.”;   uses t128ext:access-policy;  }  ... }

Any multicast service needs a source that generates the multicastpacket. The sender policy imposes access policies on the sender. In theexample above, the sender-policy allows tenant red. This means that thesource is allowed to send packets to this multicast group if the sourceis classified as tenant red.

In an exemplary embodiment, multicast-listeners can be configured on aninterface. By default, the receivers (a.k.a. listeners) will be setupbased on the tenant-based access-policies that match the interfacetenant. However, there may be cases where this needs to be overridden ona per-interface basis. The following is an example configurationdefinition for configuring multicast listeners in an exemplaryembodiment:

list network-interface {  ...  leaf multicast-listeners {   typeenumeration {    enum disabled {     description “Multicast listenersare disabled.”;    }    enum automatic {     description      “Multicastlisteners are enabled or disabled based on the presence of multicastservices with tenant based access policies which match this interface'stenant.”;    }    enum enabled {     description “Multicast listenersare enabled.”;    }   }   default automatic;   description    “Enablesthe sending of IGMP and MLD queries on this    interface.”;   }  }  ...}

The multicast-listener configuration can be used to override the currentservice access-policy. It can be used to enable receivers to join anymulticast service using the enabled flag. It also can be used to disablelisteners on the interface even if the multicast service allows them viaaccess policies. Since tenants are authority wide in an exemplaryembodiment, this would provide more granular control of receivers incase there are outliers within some routers.

In an exemplary embodiment, there are two different deployment use casesfor the multicast services, namely Point to Multipoint SVR and MulticastProxy.

For Point-to-Multipoint SVR, an SVR path refers to secure vector routingbetween two routers, which, in an exemplary embodiment, ispoint-to-point for unicast services. But with multicast services, arouter will replicate the sourced packet to all other routers that havereceivers on them. Hence it is termed point-to-multipoint SVR. In FIG.21 , the datacenter has a multicast server behind an SSR router whichwill be the source of the multicast service. Each of the branches,branch1 and branch2, have two multicast clients, each of which are thereceivers. Consider the same service “mcast” defined in the exampleabove with a multicast address of 233.252.0.2. Each multicast clientwill send IGMP join messages to the branch routers for the multicastgroup 233.252.0.2. Hence each branch router will register two receiversfor this group. The source packet originating at the data center needsto be sent to both branches.

In a STEP environment, all STEP routers, including any STEP routers inthe PIM (Protocol Independent Multicast) cloud, can obtain informationon the multicast service and determine which router(s) and path(s) willbe used to distribute the source packet. Specifically, eachparticipating router advertises any multicast source(s) and/or multicastreceiver(s) associated with the router, and the routers can make routingdecisions (such as selecting optimal “rendezvous point” router(s) in thenetwork, e.g., the smallest tree needed to distribute the multicastpackets) based on the advertised information. For example, a routerassociated with one or more multicast receivers (referred to herein as amulticast receiver router) will advertise that it is a multicastreceiver router along with information about the multicast receivers.However, multicast services of the type described herein can besupported in a non-STEP environment, for example, by setting upservice-routes on the datacenter for each of these branch routers. Thefollowing is an example service route configuration for the networkconfiguration shown in FIG. 22 :

service-route  name : branch1_service_route  service : mcast  peer :branch1 service-route  name : branch2_service_route  service : mcast peer : branch2

With the above configuration, any packets sent by the multicast serverto the multicast group 233.252.0.2 will be forwarded to each branchrouter via an SVR path. It is important to understand that the SVR pathsmentioned here are unicast paths and not multicast. In an exemplaryembodiment, the multicast packet from the source will be sent as aunicast packet to each of the branches, using network addresstranslation (NAT) to translate the SVR IP addresses and ports for eachpath and carrying the original SVR IP addresses and ports in a metadatafield in the packet. At the branch, the metadata will be used to findthe multicast service and send the packet to all the receiversassociated with it. It should be noted that after a branch router hasreceived a unicast packet with metadata, the branch router may establishan association between the translated address/port numbers with theoriginal address/port numbers in the metadata for handling futurepackets associated with the multicast service, and thereafter the sourcecan stop sending the metadata in subsequent packets to that branchrouter in order to reduce the overhead incurred by the metadata. It alsoshould be noted that in the above example, the headend (source) routerreplicates packets to all other routers and there is no multicast treeused for this distribution of packets, and as more branch routers areadded, the headend replication can become too inefficient. Therefore, inorder to scale more efficiently, exemplary embodiments may have themulticast stream join an existing multicast tree downstream or havereplication endpoints that can replicate to other endpoints.

For multicast proxy, the routers can deliver multicast services byjoining an existing multicast tree and “proxying” packets betweenunicast and multicast. For example, with reference again to FIG. 23having the “mcast” service with address of 233.252.0.2, the datacentercan send the multicast packets into the PIM network in the middle, wherethe PIM network knows about this multicast group (e.g., in an exemplaryembodiment, the PIM network is required to have knowledge of the actualmulticast service IP address that is being replicated, and multicastaddress translation is not supported). This is different from thepoint-to-multipoint SVR environment discussed above in that thedatacenter router transmits multicast packets rather than unicastpackets and does not have to replicate the packets for unicasttransmission to multiple branches, i.e., only one copy of a sourcepacket needs to be transmitted to the PIM network. Thus, this scheme ismore scalable than the point-to-multipoint SVR scheme.

It should be noted that SSRs support encryption for point-to-point SVRpaths and therefore encryption can easily be provided in thepoint-to-multipoint SVR scheme. Providing encryption in the multicastproxy scheme is more complex because there are multiple receivers,although, for example, a common set of encryption keys can bedistributed to all receivers so that the source packets can be encryptedonce for all receivers.

The branch routers' functionality is the same as that of thepoint-to-multipoint deployment for interfaces that enable multicastlisteners. It receives IGMP reports from interfaces that allow multicastlisteners. The main difference here is that the branch routers need toforward these reports to the PIM network. In order to achieve this, theinterface can be configured to act as a multicast-report-proxy (e.g.,the tenant of the interface which is enabled for PIM proxy should beallowed in the multicast-sender-policy list). This will cause the branchrouters to join the PIM network for multicast group 233.252.0.2 and willstart receiving packets multicast from the datacenter. These packets inturn will be forwarded to the multicast receivers.

The following is example data model to set up an interface as multicastproxy:

list network-interface {  ...  leaf multicast-report-proxy {   typeboolean;   default false;   description    “Enables the forwarding ofIGMP and MLD joins/leaves/reports to valid multicast services to thisnetwork interface. These must come from other network interfaces whichallow multicast listeners.”;  }  ... }

Here, when an interface is configured for multicast-report-proxy, itwill forward all multicast reports received from any other networkinterfaces that allow multicast listeners.

In an exemplary embodiment, IGMP joins will be listed in displays of therouting information base, for example, as follows:

show rib Codes: K - kernel route, C - connected, S - static, R - RIP, O - OSPF, I - IS-IS, B - BGP, E - EIGRP, N - NHRP,  T - Table, v - VNC,V - VNC-Direct, A - Babel, D - SHARP,  F - PBR,  > - selected route, * -FIB route C>* 169.254.127.126/31 is directly connected, g4294967294,21:08:01 C>* 172.16.1.0/24 is directly connected, g1, 21:07:43 K>*224.1.2.3/32 [254/0] is directly connected, g3 ⇐= IGMP join received

Multicast Support in Step

In an exemplary embodiment, multicast services work predominantly likeany other service except that multicast services are advertised by arouter only if multicast (e.g., IGMP) joins are received for theconfigured multicast address.

FIG. 10 is a schematic diagram showing a topology including a multicastconfiguration with no receivers. In this example, router R1 is thesource. Both router R2 and router R3 are potential receivers. Initially,there are no receivers on router R2 and router R3, and therefore neitherrouter R2 nor router R3 will advertise the multicast service. As aresult, router R1 finds no service routes for this service and thereforewill not forward packets. The source packets will be dropped at routerR1.

STEP helps to discover the multicast receivers for a particular servicedynamically. There is no PIM or legacy protocols running in the core.The receivers are simply discovered as part of the multicast serviceslike any other service.

FIG. 11 is a schematic diagram showing the topology of FIG. 10 but nowwith router R2 having received IGMP joins on two of its interfaces.Router R2 will now advertise the multicast address with two serviceroutes. There are two service routes, as there are two interfaces fromwhich the IGMP joins are received. This is akin to routes being receivedfrom another routing protocol or a new service route being configured.Router R2 will stop advertising the service if it receives an IGMP leavefrom all the receivers. Since R2 will advertise the multicast service,the following is an example STEP document for router R2:

{  node : [ {   name : “node2”,   peerPaths : [ {    identifier :“R1+3.5.6.7+node2+12+0”,    hostname : “EastRouter.node2.intf”,   peerName : “peer2”,    vector : [ “mpls” ]   } ]   service : [ {   name : “S1”,    route : [ {     ipPrefix : “224.1.2.3”,    prefixLength :32,    } ],    service-route : [     {      name :“mcast-route-intf1”,      serviceNexthop : [       { vector : “red” },     ],     },     {      name : “mcast-route-intf2”,     serviceNexthop : [       { vector : “blue” },      ]     }    ]   }]  } ] }

Here, router R1 will discover via STEP that the service S1 is availableon router R2 and hence it will send all multicast traffic from thesource to router R2, which in turn will forward the packets to all thereceivers.

Service Exchange Between Districts

STEP routers publish router documents for each district for which theyare members. In the event a router is part of more than one district,the routes and services learned from one district will be aggregated andpublished to the other district with nexthop as self (i.e. a router inone district will not publish all the other peer information it haslearned to another district). This way the routers in one district willbe hidden from another district. This helps segment the network betteras all routers need not learn about all other routers in the network.

FIG. 12 is a schematic diagram showing the same topology as FIG. 6 . Inthis example, there are three districts, specifically a district named“east” including routers DC1, Br1, and Br2; a district named “west”including routers DC2, Br3, and Br4; and a district named “central”including routers DC1 and DC2. Thus, routers DC1 and DC2 are part of twodistricts.

Consider that service S1 is published by router Br1 in district east andservice S2 is published by router Br3 in district west. Branches Br1 andBr2 will not discover service S2 and branches Br3 and BR4 will notdiscover service S1. However, since routers DC1 and DC2 share the samedistrict “central,” the services from district “east” can be learned byBr3 and Br4, and vice versa.

STEP documents published by DC1 in district “central” will have theservice S1, but with a local next hop and cost. The cost here is thetotal cost of vectors to reach the service S1 on branch Br1. A similaroperation is done by router DC2 for service S1.

The following are exemplary STEP documents for each of these routers:

Router Br1   • Obtains service S1 and service route for S1 viaconfiguration   • Publishes service S1 into district east  {   node : [{    name : ″node2″,    peerPaths : [ {     identifier :″DC1+3.5.6.7+node2+12+0″,     hostname : ″R1.node2.intf″,     peerName :″DC1″,     vector : [ ″mpls″ ]    } ]    service : [ {     name : ″S1″,    route : [ {      ipPrefix : ″1.2.3.0″,      prefixLength : 24     }],     service-route : [ {      name : ″service-route1″,     serviceNexthop : [       { vector : ″red″ },      ],     } ]    } ]  } ]  } Router Br3   • Obtains service S2 and service route for S2 viaconfiguration   • Publishes service S2 into district west  {   node : [{    name : ″node2″,    peerPaths : [ {     identifier :″DC2+3.5.6.7+node2+12+0″,     hostname : ″R1.node2.intf″,     peerName :″DC2″,     ″vector″ : [ ″mpls″ ]    } ],    service : [ {     name :″S2″,     route : [ {      ipPrefix : ″5.5.5.5″,      prefixLength : 32    } ],     service-route : [ {      name : ″service-route21″,     serviceNexthop : [       { vector : ″blue″ }      ] }     } ]    }]   } ]  } Router DC1   • Learns service S2 from DC2 via district“central”   • Publishes the learned service S2 into district ”east” withassociated     cost   • Publishes service S1 into district “central”   •None of the peer topologies are exposed between districts.  DC1 documentpublished under district east  {   node : [ {    name : ″node2″,   peerPaths : [     {      identifier : ″Br1+3.5.6.7+node2+12+0″,     hostname : ″Br1.node2.intf″,      peerName : ″Br1″,      vector : [″mpls″ ]     },     {      identifier : ″Br2+3.5.6.7+node2+12+0″,     hostname : ″Br2.node2.intf″,      peerName : ″Br2″,      vector : [″mpls″ ]     }    ],    service : [ {     name : ″S2″,     route : [ {     ipPrefix : ″5.5.5.5″,      prefixLength : 32,      nexthop : [ {cost : 20} ]     } ]    } ]   } ]  }  DC1 document published underdistrict central.  {   node : [ {    name : ″node2″,    peerPaths : [ {    identifier : ″DC2+3.5.6.7+node2+12+0″,     hostname :″DC2.node2.intf″,     peerName : ″DC2″,     vector : [″internet″]    }],    service : [ {     name : ″S1″,     route : [ {      ipPrefix :″1.2.3.0″,      prefixLength : 24,      nexthop : [ { cost : 10} ]     }]    } ]   } ]  } Router DC3   • Learns service S1 from DC2 via district“central”   • Publishes the learned service S1 into district “west” withassociated     cost   • Publishes service S2 into district “central”   •None of the peer topologies are exposed between districts  DC2 documentpublished under district west  {   node : [ {    name : ″node2″,   peerPaths : [     {      identifier : ″Br3+3.5.6.7+node2+12+0″,     hostname : ″Br3.node2.intf″,      peerName : ″Br3″,      vector : [″mpls″ ]     },     {      identifier : ″Br4+3.5.6.7+node2+12+0″,     hostname : ″Br4.node2.intf″,      peerName : ″Br4″,      vector :[″mpls″]     }    ],    service : [ {     name : ″S1″,     route : [ {     ipPrefix : ″1.2.3.0″,      prefixLength : 24,      nexthop : [ {cost : 10} ]     } ]    } ]   } ]  }  DC2 document published underdistrict central.  {   node : [ {    name : ″node2″,    peerPaths : [ {    identifier : ″DC2+3.5.6.7+node2+12+0″,     hostname :″DC2.node2.intf″,     peerName : ″DC2″,     vector : [ ″internet″ ]    }],    service : [ {     name : ″S2″,     route : [ {      ipPrefix :″5.5.5.5″,      prefixLength : 32,      nexthop : [ {cost : 20} ]     }]    } ]   } ]  }

STEP documents for routers Br2 and Br4 are not being provided, as theyare not advertising any services.

The above example illustrates how services can be learned and advertisedbetween districts. It is possible that the same service S1 could belearned from district west via DC2. That just means that service S1 isalso available in district west. For all routers in district east, itwill just show up as another nexthop on DC1.

FIG. 18 is a logic flow diagram for publishing an aggregated route orservice, in accordance with one exemplary embodiment. In block 1902, afirst router receives service and topology state information for atleast one other router. In block 1904, the first router identifies,using the received service and topology state information, a route orservice from another router for which access to the route or service isavailable to a second router through the first router. In block 1906,the first router computes an aggregated metric for the route or serviceavailable through the first router. In block 1908, the first routerpublishes the route or service including the aggregated metric and thefirst router as the nexthop for the published route or service. Incertain exemplary embodiments, the first router publishes the route orservice by transmitting the route or service to a central repositorythat is configured to convey the route or service to the second router.As discussed herein the first router may be a member of a first districtand a second district, the second router may be a member of the seconddistrict, the first router may receive the service and topology stateinformation from at least one other router in the first district, andthe first router may publish the route or service to the second routerin the second district in a manner that hides, from the second router,information from the first district relating to the route or service.

Loop Prevention with Step

Service exchange between districts could cause one district to relearnwhat it had advertised into another district and as a result could causea routing loop. FIG. 13 is a schematic diagram showing a topologyincluding a service exchange between districts that causes a loop. Inthis example, router R2 hosts a service route SR1 for service S1 andadvertises it to router R3. Router R3 in turn advertises it to routerR2, which is in district west. Router R3 then advertises it back torouter R2. Thus, when router R2 receives the update from router R1, itwould think there is another path available for service S1 which is viarouter R1, while in reality router R2 had received its ownadvertisement. The same could happen in the direction from router R2 torouter R1. In that case, router R2 will receive the update from routerR3. This causes a loop in the network.

To prevent loops, the router source path is appended to each routeadvertised into the other district. The loop prevention algorithm is asfollows:

-   -   Each router that advertises aggregated routes and services from        one district to another will append the district name from where        the service/route was aggregated as part of the nexthop. As        services are distributed throughout the network, the district        paths will get appended to the nexthop.    -   If a router receives service prefixes/routes with a district in        the source path and the router is a member of the district, the        router will ignore that prefix/nexthop.

This will ensure that the same service prefixes advertised by onedistrict will not come back to itself via another district.

FIG. 14 is a schematic diagram showing the topology of FIG. 13 butincluding service exchange between districts with loop avoidance. Inthis example, router R2 has service route SR1 in district “south” forservice S1. The following happens:

-   -   R2 advertises S1 in district central, appending district south        from where the SR1 was learned. The source path list will have        [south]    -   R3 advertises S1 in district west, appending district central        from where SR1 was learned. The source path list will have        [south, central]    -   R1 advertises S1 in district east, appending district west from        where SR1 was learned. The source path list will have [south,        central, west]    -   R2 learns the service S1 from district east and finds that        district south, which it belongs to, is already in the        advertised service route and hence will ignore it. This avoids        the loop.

FIG. 19 is a logic flow diagram for loop detection and prevention, inaccordance with one exemplary embodiment. In block 2002, a given routerin a first district publishes a first route or service from the firstdistrict to a second district by transmitting a first publicationincluding the first route or service and a first source path for thefirst route or service with the first district name included in thefirst source path. In block 2004, the given router receives from anotherdistrict a publication of a second route or service including a secondsource path. In block 2006, the given router determines if the secondsource includes the first district name. In block 2008, the given routerprocesses the second route or service as a newly learned route orservice in the first district when the second source path does notinclude the first district name. In block 2010, the given router ignoresthe second route or service when the second source path does include thefirst district name.

Source-Based Routing with Step

STEP will support the use of source-based routing to route packets inthe network. In source-based routing, the source router of a packet orgroup of related packets (such as for a TCP or other communicationsession) determines the path to be taken by the packet(s) based on itsrouting algorithm, taking into account service and topology stateinformation received for one or more other routers via STEP. The sourcerouter includes a metadata field in the packet (or, typically, in thefirst packet of a session), where the metadata field specifies therouters through which the packet(s) are to be carried, e.g., in the formof a router list. Each router along the path (referred to herein as a“waypoint” router) examines the metadata to identify the next intendedrouter on the path and modifies the packet to forward the packet to thenext intended router, e.g., by modifying the destination address of thepacket to be the address of the next intended router. The waypointrouter typically also modifies the source address of the packet to bethe address of the waypoint router itself, and may modify other fieldsof the packet, e.g., source port, destination port, and protocol fields.Original source and destination addressing information for a sessionalso may be carried in the packet as metadata so that each waypointrouter can associate the packets with a particular session and so thatthe final router along the path can revert the source and destinationaddress information in the packet back to the original source anddestination address information. These operations are described, forexample, in related U.S. patent application Ser. No. 14/833,571, nowissued U.S. Pat. No. 9,762,485, which was incorporated by referenceabove, although it should be noted that with source-based routing, theintermediate waypoint routers are not required to select a next waypointrouter but instead obtain the next waypoint router from the metadata inthe received packet. As part of this process, the waypoint router canremove itself from the router list in the packet metadata so that onlyany remaining waypoint routers along the intended path remain in therouter list, although this technically is not required (and, in someembodiments, the waypoint router may be excluded from the router listbecause the waypoint router is implicitly included in the path by virtueof receiving the packet). Each waypoint router typically alsoestablishes forward (and optionally also reverse) associationinformation to associate the session packet(s) with the specified pathso that subsequent packets associated with the session, which generallydo not include the metadata field, can be identified and forwarded alongthe specified path. The last waypoint router on the path forwards thepacket to its intended destination, typically also removing the metadatafield from the packet and reinstating the original source anddestination addresses for the packet. Subsequent packets associated withthe session traverse the waypoint routers based on the forward (andoptionally reverse) association information. Examples of such forwardand reverse association information and forwarding of packets based onforward and reverse association information are described in relatedU.S. patent application Ser. No. 14/833,571, now issued U.S. Pat. No.9,762,485, which was incorporated by reference above.

Segment routing is very powerful to interact between variousheterogeneous networks. STEP goes one step further in providing servicelevel routing separation (i.e., on a per service basis, all paths maynot be available to all routers). The service path availability view ofone router could be different from that of the advertising router.Therefore, in an exemplary embodiment, is imperative for the router listchosen by the source router to be honored by the other routers.

FIG. 15 is a schematic diagram showing a topology including source-basedrouting within the same district. In this example, router R1 determinesthat the path to be traversed for service S1 is via R2 and R4. Router R1will add R2 and R4 to the router list in its metadata. There is a pathto router R4 from router R2 via router R3, but because router R2inspects the metadata in the packet, it will honor the router list andforward the packet to R4 instead of R3. It should be noted that therouter list sent by router R1 could exclude router R2, because router R1sends the packet to router R2 so including router R2 in the router listcould be seen as redundant. Similarly, the router list sent by router R2could exclude router R4 because router R2 sends the packet to router R4so including router R4 in the router list could be seen as redundant.Alternatively, assuming a router would never show up in the router listtwice, the router list could remain intact as the packet is propagatedfrom router to router, with each router simply examining the router listfor itself and then identifying the next router (if any) to receive thepacket.

FIG. 15 is a simple example that demonstrates how the source-basedrouting works in an exemplary embodiment. Without source-based routing,R2 would make an independent routing decision, which could have sent thepacket to R3 and R3 possibly could have sent the packet back to R1.Thus, source-based routing can aid in loop prevention.

In an exemplary embodiment, when access to a route or service crossesmultiple districts, the router list in the metadata does not crossdistrict boundaries. FIG. 16 is a schematic diagram showing a topologyincluding source-based routing across multiple districts. In thisexample, router R1 determines that the path to be traversed for serviceS1 in district east is via router R2. Thus, router R1 sends a packetwith a router list (R2) to router R2 in district east. Router R2 popsitself from the metadata, determines a path to router R3 via router R4within district west, adds a new router list (R4, R3) based on the pathit calculates to get to the final destination in district west, andforwards the packet with the new router list to router R4. Router R4removes itself from the metadata and passes on (R3) in the router listto router R3. Router R3 removes itself from the router-list and, seeingthat it is the last router in the list, sends the packet to the finaldestination. Here, the router list in the metadata does not crossdistrict boundaries. Each router will only route packets among routerswithin the same district. When packets cross districts, a new routerlist will be added in order to continue source-based routing if needed.

It should be noted that metadata handling is backward compatible. Anyexisting routers will ignore the new metadata field and will function asit does today. Any packets received in the new routers with STEP enabledwill forward the packet to the next available destination if the packetcomes without the router list metadata (e.g. coming from a non-STEPenabled router).

FIG. 20 is a logic flow diagram for source-based routing, in accordancewith an exemplary embodiment. In block 2102, the source routerdetermines a path for a route or service including an ordered list ofsuccessive routers to receive a packet associated with the route orservice starting with a first successive router and ending with adestination router. In block 2104, the source router transmits thepacket toward the first successive router with a metadata fieldincluding a list of at least one remaining router of the ordered list ofrouters to receive the packet associated with the route or service. Inblock 2106, each successive router, starting with the first successiverouter, determines if the router is the destination router and forwardsthe packet toward a next successive router in the ordered list ofrouters if the router is not the destination router. The source routermay be configured to include the first successive router in the metadatafield or to exclude the first successive router from the metadata field.Each successive router may be configured to remove itself from themetadata field before forwarding the packet to the next successiverouter. Each successive router may be configured to forward the packetto the next successive packet by changing the destination address of thepacket to an address of the next successive router and optionally alsoto change the source address of the packet to an address of the router.The destination router may be configured to remove the metadata fieldfrom the packet and forward the packet to the destination.Alternatively, the destination router may be configured to determine asecond path to the destination for the route or service, the second pathincluding a second ordered list of successive routers to receive thepacket associated with the route or service, and to transmit the packeta new metadata field including a list of at least one remaining routerof the second ordered list of routers to receive the packet associatedwith the route or service.

It should be noted that source-based routing may be used in one districtbut not in another district. For example, with reference again to FIG.16 , router R1 could use source-based routing within district east butrouter R2 could use a different routing scheme within district west(e.g., using traditional routing including STEP-enhanced routing, orusing another routing construct such as MPLS), or vice versa.

Network Evaluation with Step

The STEP repository has STEP documents from all STEP routers in thenetwork, advertising their service availability. This means the STEPrepository can provide a view of the whole network at any given time andalso can provide a history of the changes that happened in the networkover a period of time.

In an exemplary embodiment, the user interface (e.g., web client) willbe enhanced to provide service level and network level views, relativeto the data contained within the STEP repository. Since the STEPrepository is non-persistent, a STEP monitoring client on the Conductorwill listen to all STEP changes in the network and store them in apersistent time series database. The raw data would be stored andaggregated for configured amount of time. There will also be aninterface for viewing the contents of the STEP repository, e.g., todebug routing issues.

The following is an example of a “show” command that lists all STEPrepositories and the number of clients connected to each:

show STEP repos Location Address Uptime Priority Clients Router DC11.2.3.4 12 h 10 100 (primary) Conductor 2.3.4.5 10 h 8 20 Router DC21.3.4.5  2 h 9 0

Location indicates where these STEP repositories are hosted. The primaryrepository is where all records are stored. All other repositories proxyrequests to the primary. The Clients section indicates the number ofclients connected to each repository. On the primary repository, thenumber of clients preferably includes the proxied requests from theother STEP repositories.

The following is an example of a “summary” command that shows the numberof districts and number of routers per district.

show STEP repo summary Authority : t128 Districts : 2  Name Routers District A 4  District B 2 Client Connections : 6

Each router repository can be queried independently to see the currentstate advertised by each router. It shows each district that the routeris member of and the advertisement made by the router in each of thosedistricts.

show STEP repo router R1 <district> District A  PeerPaths:  Peer-path-id1    SLA(updated 2min ago)     Latency : 20ms     Loss :0%     Jitter : 10ms    Service Policies     Policy1 : meets SLA    Policy2 : does not meet SLA  Services :   Service S1    1.1.1.0/24nexthop { vector A }    1.1.1.1/32 nexthop { vector B, sourcePath :DistrictB }   Service S2    1.1.1.0/24 nexthop { vector A }  ExternalRoutes:   Protocols    BGP     5.5.5.5/32 nexthop { cost 1, sourcePath :DistrictB }  District B   PeerPaths:    Peer-path-id2     SLA (updated3min ago)      Latency : 10ms      Loss : 1%      Jitter : 0ms    Service Policies       Policy1 : meets SLA       Policy2 : meets SLA Services :   Service S1    1.1.1.1/32 nexthop { vector B }

The previous commands provide the network overview from each router'sperspective. While troubleshooting problems in the network, the lastchanges that happened in the network will be more useful than the wholenetwork view. The following command shows the last changes. Thefollowing is an example of showing the last changes.

show STEP repo updates <district> <num last updates> District A  1 minago   + R1    Service S1     1.1.1.0/24 nexthop { vector A }   − R2   External Routes 2.2.2.2/24 nexthop { cost 1 }  2 min ago   +  R3   peer-path-id1 Service Policies  Policy 1 : does not meet SLA ...

The user interface (e.g., web client) will be enhanced to show thehistory of STEP repository changes. The STEP repository has the diff ofall network topology changes per district. So, the network topologychanges at any point of time can be replayed on the web to show therouter changes, path SLA changes, and network outages. This will serveas very powerful tool to monitor network changes and pinpoint outagesduring a specific period of time.

FIG. 17 is a schematic wire frame diagram showing a heatmap view of thenetwork.

Aggregated Routes and Services

As discussed above, in the event a router is part of more than onedistrict, the routes or services learned from a first district will beaggregated and published to a second district with the router as thenexthop for the aggregated routes or services (i.e., a router in onedistrict will not publish all the other peer information it has learnedto another district). In this way, the routers in the first districtwill be hidden from the second district, i.e., routers in the seconddistrict will know that the route or service is available from therouter in the first district that advertised the route or service, butwill not have a view into the specific way in which the route or serviceis provided in the first district. This helps to better segment thenetwork, as the routers in the second district need not learn about allof the routers in the first district.

Furthermore, the router can publish the aggregated route or service withan aggregated path metric, allowing routers in the second district toevaluate the aggregated route or service as an entity without knowingdetails of the route or service in the first district.

Additionally or alternatively, in order to prevent loops, the router inthe first will append the first district name to the source path of thepublished route or service. Then, if a router in the first districtreceives a publication of the route or service from another district andthe first district name is in the source path of the published route orservice, the router will ignore the published route or service.

It should be noted that routers in the second district may receivepublications of a particular aggregated route or service from multiplerouters in the first district, and each can have a different pathmetric. Thus, for example, if a particular route or service is availablethrough two routers in a particular district, routers in other districtscan select the router having the best metric for the particular route orservice.

Alternative Publication Mechanisms

Exemplary STEP embodiments are described above with reference to apublish-subscribe model in which the STEP routers publish STEP documentsto the STEP server and subscribe to the STEP server to receive serviceand topology state information from other routers. However, inalternative embodiments, STEP can be implemented using other mechanismsto selectively distribute service and topology state information amongand between routers to accomplish essentially the same functionality asdescribed above.

For one example, the STEP server can be configured to implement a “push”mechanism for selectively transmitting service and topology stateinformation to the routers. Here, for example, rather than the STEProuters subscribing to receive service and topology state information,the STEP router can distribute the service and topology stateinformation received from the STEP routers based on configurationinformation without the STEP routers subscribing to receive the serviceand topology state information.

For another example, STEP routers can exchange service and topologystate information through a mesh transfer mechanism based onconfiguration information. Here, for example, each STEP router can beconfigured exchange service and topology state information with one ormore other STEP routers (including in multiple districts), and the STEProuters then can establish peer-to-peer direct or indirect communicationconnections to exchange the service and topology state information.

For another example, STEP routers can exchange service and topologystate information through a peer-to-peer transfer mechanism in whichSTEP routers pass along service and topology state information to otherSTEP routers so that all STEP routers obtain the service and topologystate information for the other STEP routers from which the service andtopology state information is needed. For example, if router A has anadjacency to router B and router B has an adjacency to router C, thenrouter C could transfer its own service and topology state informationand optionally other collected service and topology state information torouter B, which in turn could transfer its own service and topologystate information as well as service and topology state informationreceived from router C to router A.

Thus, STEP generally involves the selective distribution of service andtopology state information among and between STEP routers so that theSTEP routers can have additional information on which to make routingdecisions and can be implemented using a variety of distributionmechanisms.

It also should be noted that many of the applications described abovecan be supported in non-STEP routing systems through other publicationmechanisms. For example, a non-STEP router can advertise an aggregatedroute or service to an adjacent router, e.g., as part of a link-stateexchange.

Miscellaneous

It should be noted that headings are used above for convenience and arenot to be construed as limiting the present invention in any way.

Various embodiments of the invention may be implemented at least in partin any conventional computer programming language. For example, someembodiments may be implemented in a procedural programming language(e.g., “C”), or in an object oriented programming language (e.g.,“C++”). Other embodiments of the invention may be implemented as apre-configured, stand-along hardware element and/or as preprogrammedhardware elements (e.g., application specific integrated circuits,FPGAs, and digital signal processors), or other related components.

In an alternative embodiment, the disclosed apparatus and methods (e.g.,see the various flow charts described above) may be implemented as acomputer program product for use with a computer system. Suchimplementation may include a series of computer instructions fixedeither on a tangible, non-transitory medium, such as a computer readablemedium (e.g., a diskette, CD-ROM, ROM, or fixed disk). The series ofcomputer instructions can embody all or part of the functionalitypreviously described herein with respect to the system.

Those skilled in the art should appreciate that such computerinstructions can be written in a number of programming languages for usewith many computer architectures or operating systems. Furthermore, suchinstructions may be stored in any memory device, such as semiconductor,magnetic, optical or other memory devices, and may be transmitted usingany communications technology, such as optical, infrared, microwave, orother transmission technologies.

Among other ways, such a computer program product may be distributed asa removable medium with accompanying printed or electronic documentation(e.g., shrink wrapped software), preloaded with a computer system (e.g.,on system ROM or fixed disk), or distributed from a server or electronicbulletin board over the network (e.g., the Internet or World Wide Web).In fact, some embodiments may be implemented in a software-as-a-servicemodel (“SAAS”) or cloud computing model. Of course, some embodiments ofthe invention may be implemented as a combination of both software(e.g., a computer program product) and hardware. Still other embodimentsof the invention are implemented as entirely hardware, or entirelysoftware.

Computer program logic implementing all or part of the functionalitypreviously described herein may be executed at different times on asingle processor (e.g., concurrently) or may be executed at the same ordifferent times on multiple processors and may run under a singleoperating system process/thread or under different operating systemprocesses/threads. Thus, the term “computer process” refers generally tothe execution of a set of computer program instructions regardless ofwhether different computer processes are executed on the same ordifferent processors and regardless of whether different computerprocesses run under the same operating system process/thread ordifferent operating system processes/threads.

Importantly, it should be noted that embodiments of the presentinvention may employ conventional components such as conventionalcomputers (e.g., off-the-shelf PCs, mainframes, microprocessors),conventional programmable logic devices (e.g., off-the shelf FPGAs orPLDs), or conventional hardware components (e.g., off-the-shelf ASICs ordiscrete hardware components) which, when programmed or configured toperform the non-conventional methods described herein, producenon-conventional devices or systems. Thus, there is nothing conventionalabout the inventions described herein because even when embodiments areimplemented using conventional components, the resulting devices andsystems (e.g., the STEP server controller and STEP client controller)are necessarily non-conventional because, absent special programming orconfiguration, the conventional components do not inherently perform thedescribed non-conventional functions.

The activities described and claimed herein provide technologicalsolutions to problems that arise squarely in the realm of technology.These solutions as a whole are not well-understood, routine, orconventional and in any case provide practical applications thattransform and improve computers and computer routing systems.

Potential Claims

Various embodiments of the present invention may be characterized by thepotential claims listed in the paragraphs following this paragraph (andbefore the actual claims provided at the end of the application). Thesepotential claims form a part of the written description of theapplication. Accordingly, subject matter of the following potentialclaims may be presented as actual claims in later proceedings involvingthis application or any application claiming priority based on thisapplication. Inclusion of such potential claims should not be construedto mean that the actual claims do not cover the subject matter of thepotential claims. Thus, a decision to not present these potential claimsin later proceedings should not be construed as a donation of thesubject matter to the public.

Without limitation, potential subject matter that may be claimed(prefaced with the letter “P” so as to avoid confusion with the actualclaims presented below) relating to a service and topology exchangeprotocol includes:

P1. A routing system for implementing a service and topology exchangeprotocol (STEP), the routing system comprising:

-   -   a primary STEP server configured to maintain a STEP repository;        and    -   a plurality of routers, each router including a STEP client in        communication with the primary STEP server; wherein:    -   the STEP client of each router is configured to transmit, using        the service and topology exchange protocol, STEP documents        containing service and topology state information for at least        one route or service available through the router to the primary        STEP server for storage in the STEP repository;    -   the primary STEP server is configured to transmit to the STEP        client of each router, using the service and topology exchange        protocol, service and topology state information from the STEP        repository for at least one other router based on configured        relationships between routers; and each router is configured to        make routing decisions based at least in part on the service and        topology state information from the at least one other router.

P2. The system of claim P1, wherein the STEP documents include JSONpatch documents.

P3. The system of claim P1, wherein the information in the STEPrepository is organized as a path tree database and wherein each STEPdocument includes a path definition identifying the router for storageof the router's service and topology state information in the path treedatabase.

P4. The system of claim P1, further comprising at least one secondarySTEP server that is configured to proxy STEP requests to the primarySTEP server.

P5. The system of claim P1, wherein at least one router is a member of aplurality of districts and transmits a separate STEP document containingservice and topology state information for each district of which it isa member.

P6. The system of claim P1, wherein at least one router is a member of aplurality of districts and receives service and topology stateinformation for routers in each district of which it is a member.

P7. The system of claim P1, wherein the service and topology stateinformation transmitted by the router further includes a service levelagreement for a given service and an indication of whether or not thegiven service is within the service level agreement.

P8. The system of claim P1, wherein at least one router is a member of adistrict and transmits service and topology state information includinga route or service learned from outside of the district.

P9. The system of claim P1, wherein at least one router transmitsservice and topology state information including at least one pathmetric for a route or service.

P10. The system of claim P1, wherein the primary STEP server is separatefrom the routers.

P11. The system of claim P1, wherein the primary STEP server is in oneof the routers.

P12. A server for implementing a service and topology exchange protocol(STEP), the server comprising:

-   -   a datastore; and    -   a service and topology exchange protocol (STEP) server        controller in communication with a plurality of routers, the        STEP server controller configured to:        -   maintain a STEP repository in the datastore;        -   receive, from each of the plurality of routers, using the            service and topology exchange protocol, STEP documents            containing service and topology state information for            storage in the STEP repository; and        -   transmit, to each router, using the service and topology            exchange protocol, service and topology state information            from the STEP repository for at least one other router based            on configured relationships between routers, the transmitted            service and topology state information enabling each router            to make routing decisions based at least in part on the            service and topology state information from the at least one            other router.

P13. The server of claim P12, wherein the STEP documents include JSONpatch documents.

P14. The server of claim P12, wherein the information in the STEPrepository is organized as a path tree database and wherein each STEPdocument includes a path definition identifying the router for storageof the router's service and topology state information in the path treedatabase.

P15. The server of claim P12, wherein at least one router is a member ofa plurality of districts and transmits a separate STEP documentcontaining service and topology state information for each district ofwhich it is a member.

P16. The server of claim P12, wherein at least one router is a member ofa plurality of districts and receives service and topology stateinformation for routers in each district of which it is a member.

P17. The server of claim P12, wherein the server is separate from therouters.

P18. The server of claim P12, wherein the server is in one of therouters.

P19. A router for implementing a service and topology exchange protocol(STEP), the router comprising:

-   -   a datastore;    -   a service and topology exchange protocol (STEP) client        controller in communication with a STEP server, the STEP client        controller configured to:        -   transmit, using the service and topology exchange protocol,            service and topology state information for at least one            route or service available through the router to the STEP            server;        -   receive, from the STEP server, using the service and            topology exchange protocol, service and topology state            information for at least one other router based on            configured relationships between routers; and        -   store the received service and topology state information            for the at least one other router in the datastore; and    -   a routing engine configured to make routing decisions based at        least in part on the service and topology state information for        the at least one other router.

P20. The router of claim P19, wherein the STEP documents include JSONpatch documents.

P21. The router of claim P19, wherein the information in the STEPrepository is organized as a path tree database and wherein each STEPdocument includes a path definition identifying the router for storageof the router's service and topology state information in the path treedatabase.

P22. The router of claim P19, wherein the router is a member of aplurality of districts and transmits a separate STEP document containingservice and topology state information for each district of which it isa member.

P23. The router of claim P19, wherein the router is a member of aplurality of districts and receives service and topology stateinformation for routers in each district of which it is a member.

P24. The router of claim P19, wherein the service and topology stateinformation transmitted by the router further includes a service levelagreement for a given service and an indication of whether or not thegiven service is within the service level agreement.

P25. The router of claim P19, wherein the router is a member of adistrict and transmits service and topology state information includinga route or service learned from outside of the district.

P26. The router of claim P19, wherein the service and topology stateinformation transmitted by the router includes at least one metric forthe route or service.

P27. The router of claim P19, wherein the router further comprises aSTEP server configured to maintain a STEP repository.

P28. The system of claim P1, wherein a given STEP document includes onlyservice and topology state information changes.

P29. The system of claim P1, wherein given service and topology stateinformation transmitted by the primary STEP server to the STEP client ofa given router includes only service and topology state informationchanges.

P30. The server of claim P12, wherein a given STEP document includesonly service and topology state information changes.

P31. The server of claim P12, wherein given service and topology stateinformation transmitted by the primary STEP server to the STEP client ofa given router includes only service and topology state informationchanges.

P32. The router of claim P19, wherein a given STEP document includesonly service and topology state information changes.

P33. The router of claim P19, wherein given service and topology stateinformation transmitted by the primary STEP server to the STEP client ofa given router includes only service and topology state informationchanges.

Without limitation, potential subject matter that may be claimed(prefaced with the letter “P” so as to avoid confusion with the actualclaims presented below) relating to metrics on a segment basis includes:

P1. A routing system comprising:

-   -   a first router; and    -   a second router, wherein the first router is configured to        receive service and topology state information for at least one        other router; identify, using the received service and topology        state information, a route or service from another router for        which access to the route or service is available to the second        router through the first router; compute an aggregated metric        for the route or service available through the first router; and        publish the route or service to the second router including the        aggregated metric and the first router as the nexthop for the        published route or service.

P2. The system of claim P1, wherein the first router publishes the routeor service by transmitting the route or service to a central repositorythat is configured to convey the route or service to the second router.

P3. The system of claim P1, wherein:

-   -   the first router is a member of a first district and a second        district;    -   the second router is a member of the second district;    -   the first router receives the service and topology state        information from at least one other router in the first        district; and    -   the first router publishes the route or service to the second        router in the second district in a manner that hides, from the        second router, information from the first district relating to        the route or service.

P4. The system of claim P3, wherein the route or service is in the firstdistrict.

P5. The system of claim P3, wherein the route or service is in a thirddistrict.

P6. The system of claim P3, wherein the first district is associatedwith a first district name, and wherein the first router is configuredto publish the route or service to the second router in the seconddistrict including a source path for the published route or service withthe first district name included in the source path.

P7. The system of claim P6, wherein the first router is configured toreceive the published route or service including the source path fromanother district and to append the first district name to the sourcepath.

P8. A router comprising:

-   -   a datastore; and    -   a service and topology exchange protocol (STEP) client        controller configured to:        -   receive service and topology state information for at least            one other router and store the received service and topology            state information in the datastore;        -   identify, using the received service and topology state            information, a route or service from another router for            which access to the route or service is available to a            second router through the first router;        -   compute an aggregated metric for the route or service            available through the router; and        -   publish the route or service to the second router including            the aggregated metric and the router as the nexthop for the            published route or service.

P9. The router of claim P8, wherein the STEP client controller isconfigured to publish the route or service by transmitting the route orservice to a central repository that is configured to convey the routeor service to the second router.

P10. The router of claim P8, wherein:

-   -   the router is a member of a first district and a second        district;    -   the second router is a member of the second district;    -   the router receives the service and topology state information        from at least one other router in the first district; and    -   the router publishes the route or service to the second router        in the second district in a manner that hides, from the second        router, information from the first district relating to the        route or service.

P11. The router of claim P10, wherein the route or service is in thefirst district.

P12. The router of claim P10, wherein the route or service is in a thirddistrict.

P13. The router of claim P10, wherein the first district is associatedwith a first district name, and wherein the router is configured topublish the route or service to the second router in the second districtincluding a source path for the published route or service with thefirst district name included in the source path.

P14. The router of claim P13, wherein the router is configured toreceive the published route or service including the source path fromanother district and to append the first district name to the sourcepath.

P15. A routing system for detecting and avoiding loops between aplurality of routers organized into a plurality of districts, therouting system comprising:

-   -   a plurality of routers organized into a plurality of districts        including at least a first district and a second district, each        district associated with a distinct district name, the plurality        of routers including a first router that is a member of the        first district and the second district, the first router        configured to:    -   publish a first route or service from the first district to the        second district by transmitting a first publication including        the first route or service and a first source path for the first        route or service with the first district name included in the        first source path;    -   receive from another district a second publication of a second        route or service including a second source path;    -   determine if the second source path includes the first district        name;    -   process the second route or service as a newly learned route or        service in the first district when the second source path does        not include the first district name; and    -   ignore the second route or service when the second source path        does include the first district name.

P16. The system of claim P15, wherein the first route or servicepublished by the first router further identifies the first router as anexthop for the first route or service in the first district.

P17. The system of claim P15, wherein publishing the first route orservice from the first district to the second district comprises:

-   -   receiving the first publication from another district including        the first source path; and    -   appending the first district name to the first source path in        the first publication.

P18. The system of claim P15, wherein the first router transmits thefirst publication to a central repository that is configured to conveythe route or service to at least one router in the second district andreceives the second publication from the central repository.

P19. A router for detecting and avoiding loops between a plurality ofrouters organized into a plurality of districts including at least afirst district and a second district, each district associated with adistinct district name, the router being a member of the first districtand the second district, the router comprising:

-   -   a controller configured to:        -   publish a first route or service from the first district to            the second district by transmitting a first publication            including the first route or service and a first source path            for the first route or service with the first district name            included in the first source path;        -   receive from another district a second publication of a            second route or service including a second source path;        -   determine if the second source path includes the first            district name;        -   process the second route or service as a newly learned route            or service in the first district when the second source path            does not include the first district name; and        -   ignore the second route or service when the second source            path does include the first district name.

P20. The router of claim P19, wherein the first route or servicepublished by the controller further identifies the first router as anexthop for the first route or service in the first district.

P21. The router of claim P19, wherein publishing the first route orservice from the first district to the second district comprises:

-   -   receiving the first publication from another district including        the first source path; and    -   appending the first district name to the first source path in        the first publication.

P22. The router of claim P19, wherein the first router transmits thefirst publication to a central repository that is configured to conveythe route or service to at least one router in the second district andreceives the second publication from the central repository.

Without limitation, potential subject matter that may be claimed(prefaced with the letter “P” so as to avoid confusion with the actualclaims presented below) relating to distribution of multicastinformation includes:

P1. A routing system for distributing multicast routing information fora multicast service, the routing system comprising:

-   -   a plurality of routers including a multicast source router and a        plurality of multicast receiver routers, the plurality of        routers providing a multicast service, wherein the routers are        configured to exchange multicast information associated with the        multicast service including identification of multicast sources        and the multicast receivers.

P2. The system of claim P1, wherein each router is configured totransmit, using a service and topology exchange protocol (STEP), therouter's multicast information to a STEP repository and to receive fromthe STEP repository multicast information for the other routers.

P3. The system of claim P2, wherein the central repository is managed bya primary STEP server.

P4. The system of claim P3, wherein the primary STEP server is in one ofthe routers.

P5. The system of claim P3, wherein the primary STEP server is in adevice separate from the routers.

P6. The system of claim P2, wherein the multicast information istransmitted to the STEP server in STEP documents.

P7. The system of claim P6, wherein the STEP documents are JSONdocuments.

P8. The system of claim P6, wherein the information in the STEPrepository is organized as a path tree database and wherein each STEPdocument includes a path definition identifying the router for storageof the router's multicast information in the path tree database.

P9. The system of claim P1, wherein:

-   -   the multicast sources comply with a tenant-based sender access        policy that specifies at least one source tenant that is allowed        to send packets to the multicast service; and    -   the multicast receivers comply with a tenant-based receiver        access policy that specifies at least one receiver tenant that        is allowed to receive packets from the multicast service.

P10. The system of claim P1, wherein the routers are configured todetermine, based on the exchanged multicast information, an optimalrendezvous point router for distributing the packets associated with themulticast service.

P11. A router for distributing multicast routing information for amulticast service, the router comprising:

-   -   a datastore storing multicast information associated with the        multicast service including identification of multicast sources        and the multicast receivers; and    -   a controller configured to exchange multicast information        associated with the multicast service including identification        of multicast sources and the multicast receivers.

P12. The system of claim P11, wherein each router is configured totransmit, using a service and topology exchange protocol (STEP), therouter's multicast information to a STEP repository and to receive fromthe STEP repository multicast information for the other routers.

P13. The system of claim P12, wherein the central repository is managedby a primary STEP server.

P14. The system of claim P13, wherein the primary STEP server is in oneof the routers.

P15. The system of claim P13, wherein the primary STEP server is in adevice separate from the routers.

P16. The system of claim P12, wherein the multicast information istransmitted to the STEP server in STEP documents.

P17. The system of claim P16, wherein the STEP documents are JSONdocuments.

P18. The system of claim P16, wherein the information in the STEPrepository is organized as a path tree database and wherein each STEPdocument includes a path definition identifying the router for storageof the router's multicast information in the path tree database.

P19. The system of claim P11, wherein:

-   -   the multicast sources comply with a tenant-based sender access        policy that specifies at least one source tenant that is allowed        to send packets to the multicast service; and    -   the multicast receivers comply with a tenant-based receiver        access policy that specifies at least one receiver tenant that        is allowed to receive packets from the multicast service.

P20. The system of claim P11, wherein the routers are configured todetermine, based on the exchanged multicast information, an optimalrendezvous point router for distributing the packets associated with themulticast service.

Without limitation, potential subject matter that may be claimed(prefaced with the letter “P” so as to avoid confusion with the actualclaims presented below) relating to multicast source and receiver accesscontrol includes:

P1. A routing system for providing multicast access control, the routingsystem comprising:

-   -   a plurality of routers including a multicast source router and a        plurality of multicast receiver routers, the plurality of        routers providing a multicast service, wherein the routers are        configured to enforce multicast access control policies for the        multicast service including a receiver access policy that        controls which multicast receivers are allowed to receive        packets from the multicast service and a sender access policy        that controls which multicast sources are allowed to send        packets to the multicast service for distribution to the        multicast receivers.

P2. The system of claim P1, wherein the sender access policy includes atenant-based sender access policy that specifies at least one sourcetenant that is allowed to send packets to the multicast service.

P3. The system of claim P1, wherein the receiver access policy includesa tenant-based receiver access policy that specifies at least onereceiver tenant that is allowed to receive packets from the multicastservice.

P4. The system of claim P3, wherein the routers accept multicast joinsonly from interfaces associated with the at least one receiver tenant.

P5. The system of claim P3, wherein the routers accept multicast joinsonly from interfaces associated with the at least one receiver tenantunless the tenant-based receiver access policy is overridden byconfiguration on one or more interfaces.

P6. The system of claim P5, wherein at least one router is configured toaccept multicast joins from an interface that is not a specifiedreceiver tenant.

P7. The system of claim P5, wherein at least one router is configured toreject multicast joins from an interface that is a specified receivertenant.

P8. The system of claim P3, wherein the routers are configured totransmit membership query messages on interfaces associated with the atleast one receiver tenant.

P9. The system of claim P3, wherein the routers are configured to dropmembership report messages on any interface having a tenant that doesnot have access to the multicast service.

P10. The system of claim P1, wherein the routers are configured toexchange multicast information associated with the multicast serviceincluding identification of the multicast sources and the multicastreceivers.

P11. The system of claim P10, wherein each router is configured totransmit the router's multicast information to a central repository andto receive from the central repository multicast information for theother routers.

P12. The system of claim P10, wherein at least the source router isconfigured to determine, based on the exchanged multicast information,an optimal rendezvous point router for distributing the packetsassociated with the multicast service.

P13. The system of claim P1, wherein the multicast source router isconfigured to transmit unicast packets for the multicast service to eachmulticast receiver router associated with at least one multicastreceiver.

P14. The system of claim P1, wherein the multicast source router isconfigured to join a multicast tree and to transmit a multicast packetto multiple multicast receiver routers.

P15. A router for providing multicast access control, the routercomprising:

-   -   a datastore storing multicast access control policies for a        multicast service including a receiver access policy that        controls which multicast receivers are allowed to receive        packets from the multicast service and a sender access policy        that controls which multicast sources are allowed to send        packets to the multicast service for distribution to the        multicast receivers; and    -   a controller configured to enforce the multicast access control        policies for the multicast service.

P16. The router of claim P15, wherein the sender access policy includesa tenant-based sender access policy that specifies at least one sourcetenant that is allowed to send packets to the multicast service.

P17. The router of claim P15, wherein the receiver access policyincludes a tenant-based receiver access policy that specifies at leastone receiver tenant that is allowed to receive packets from themulticast service.

P18. The router of claim P17, wherein the controller is configured toaccept multicast joins only from interfaces associated with the at leastone receiver tenant.

P19. The router of claim P17, wherein the controller is configured toaccept multicast joins only from interfaces associated with the at leastone receiver tenant unless the tenant-based receiver access policy isoverridden by configuration on one or more interfaces.

P20. The router of claim P19, wherein the controller is configured toaccept multicast joins from an interface that is not a specifiedreceiver tenant.

P21. The router of claim P19, wherein the controller is configured toreject multicast joins from an interface that is a specified receivertenant.

P22. The router of claim P17, wherein the controller is configured totransmit membership query messages on interfaces associated with the atleast one receiver tenant.

P23. The router of claim P17, wherein the controller is configured todrop membership report messages on any interface having a tenant thatdoes not have access to the multicast service.

P24. The router of claim P15, wherein the controller is configured toexchange multicast information associated with the multicast servicewith other routers including identification of any multicast sources andany multicast receivers associated with the router.

P25. The router of claim P24, wherein the controller is configured totransmit the router's multicast information to a central repository andto receive from the central repository multicast information for theother routers.

P26. The router of claim P24, wherein the controller is configured todetermine, based on the exchanged multicast information, an optimalrendezvous point router for distributing the packets associated with themulticast service.

P27. The router of claim P15, wherein the controller is configured totransmit unicast packets for the multicast service to each multicastreceiver router associated with at least one multicast receiver.

P28. The router of claim P15, wherein the controller is configured tojoin a multicast tree and to transmit a multicast packet to multiplemulticast receiver routers.

Without limitation, potential subject matter that may be claimed(prefaced with the letter “P” so as to avoid confusion with the actualclaims presented below) relating to a central authority that distributesservice and topology state information changes includes:

P1. A routing system for implementing a service and topology exchangeprotocol (STEP), the routing system comprising:

-   -   a primary STEP server configured to maintain a STEP repository;        and    -   a plurality of routers, each router including a STEP client in        communication with the primary STEP server; wherein:    -   the STEP client of each router is configured to transmit, using        the service and topology exchange protocol, service and topology        state information for at least one route or service available        through the router to the primary STEP server for storage in the        STEP repository; and    -   the primary STEP server is configured to determine, for each        router, whether the STEP repository includes any service and        topology state information changes for the router based at least        in part on the service and topology state information received        from the routers and to transmit to the STEP client of each        router for which there are service and topology state        information changes, using the service and topology exchange        protocol, only the service and topology state information        changes.

P2. The system of claim P1, wherein the service and topology stateinformation changes transmitted by the primary STEP server include JSONpatch documents.

P3. The system of claim P1, wherein the information in the STEPrepository is organized as a path tree database and wherein the serviceand topology state information received from the routers includes a pathdefinition identifying the router for storage of the router's serviceand topology state information in the path tree database.

P4. The system of claim P1, further comprising at least one secondarySTEP server that is configured to proxy STEP requests to the primarySTEP server.

P5. The system of claim P1, wherein at least one router is a member of aplurality of districts and transmits separate service and topology stateinformation for each district of which it is a member.

P6. The system of claim P1, wherein at least one router is a member of aplurality of districts and receives from the primary STEP server serviceand topology state information changes for each district of which it isa member.

P7. The system of claim P1, wherein the service and topology stateinformation transmitted by the router further includes a service levelagreement for a given service and an indication of whether or not thegiven service is within the service level agreement.

P8. The system of claim P1, wherein at least one router is a member of adistrict and transmits service and topology state information includinga route or service learned from outside of the district.

P9. The system of claim P1, wherein at least one router transmitsservice and topology state information including at least one pathmetric for a route or service.

P10. The system of claim P1, wherein the primary STEP server is separatefrom the routers.

P11. The system of claim P1, wherein the primary STEP server is in oneof the routers.

P12. A server for implementing a service and topology exchange protocol(STEP), the router comprising:

-   -   a datastore; and    -   a STEP server controller in communication with a plurality of        routers, each router including a STEP client, the STEP server        controller configured to:        -   maintain a STEP repository in the datastore;        -   receive, from the STEP client of each router, using the            service and topology exchange protocol, service and topology            state information for at least one route or service            available through the router;        -   store the received service and topology state information in            the STEP repository;        -   determine, for each router, whether the STEP repository            includes any service and topology state information changes            for the router based at least in part on the service and            topology state information received from the routers; and        -   transmit to the STEP client of each router for which there            are service and topology state information changes, using            the service and topology exchange protocol, only the service            and topology state information changes.

P13. The server of claim P12, wherein the service and topology stateinformation changes transmitted by the STEP server controller includeJSON patch documents.

P14. The server of claim P12, wherein the information in the STEPrepository is organized as a path tree database and wherein the serviceand topology state information received from the routers includes a pathdefinition identifying the router for storage of the router's serviceand topology state information in the path tree database.

P15. The server of claim P12, wherein at least one router is a member ofa plurality of districts and transmits separate service and topologystate information for each district of which it is a member.

P16. The server of claim P12, wherein at least one router is a member ofa plurality of districts and receives from the STEP server controllerservice and topology state information changes for each district ofwhich it is a member.

P17. The server of claim P12, wherein the server is separate from therouters.

P18. The server of claim P12, wherein the server is in one of therouters.

Without limitation, potential subject matter that may be claimed(prefaced with the letter “P” so as to avoid confusion with the actualclaims presented below) relating to source-based routing across multipledistricts includes:

P1. A routing system for routing packets for a route or service, therouting system comprising:

-   -   a plurality of routers including a source router, wherein:    -   the source router is configured to receive, using a service and        topology exchange protocol, service and topology state        information from a STEP repository for at least one other router        based on configured relationships between routers; determine a        first path to a destination for a route or service based on the        service and topology state information, the first path including        an ordered list of successive routers to receive a packet        associated with the route or service starting with a first        successive router and ending with a destination router; and        transmit a packet toward the first successive router with first        metadata including a list of at least one remaining router of        the ordered list of routers to receive the packet associated        with the route or service; and    -   each successive router, starting with the first successive        router, is configured to receive a packet and determine if the        router is the destination router based on metadata associated        with the received packet; and when the router is not the        destination router, forward the packet toward a next successive        router in the ordered list of routers.

P2. The routing system of claim P1, wherein the source router isconfigured to include the first successive router in the first metadata.

P3. The routing system of claim P1, wherein the source router isconfigured to exclude the first successive router from the firstmetadata.

P4. The routing system of claim P1, wherein each successive router isconfigured to remove itself from the first metadata before forwardingthe packet to the next successive router.

P5. The routing system of claim P1, wherein each successive router isconfigured to forward the packet to the next successive router bychanging the destination address of the packet to an address of the nextsuccessive router.

P6. The routing system of claim P5, wherein each successive router isconfigured to forward the packet to the next successive router byfurther changing the source address of the packet to an address of theforwarding router.

P7. The routing system of claim P1, wherein the destination router isconfigured to forward the packet to the destination without metadata.

P8. The routing system of claim P1, wherein the source router isconfigured to include second metadata in the packet, the second metadataincluding session identification information.

P9. The routing system of claim P1, wherein the destination router isconfigured to determine a second path to the destination for the routeor service, the second path including a second ordered list ofsuccessive routers to receive the packet associated with the route orservice, and to transmit the packet with second metadata including alist of at least one remaining router of the second ordered list ofrouters to receive the packet associated with the route or service.

P10. A router for routing packets for a route or service, the routercomprising:

-   -   a datastore; and    -   a controller including source router logic configured to:        -   receive, using a service and topology exchange protocol,            service and topology state information from a STEP            repository for at least one other router based on configured            relationships between routers;    -   determine a first path to a destination for a route or service        based on the service and topology state information, the first        path including an ordered list of successive routers to receive        a packet associated with the route or service starting with a        first successive router and ending with a destination router;        and    -   transmit a packet toward the first successive router with first        metadata including a list of at least one remaining router of        the ordered list of routers to receive the packet associated        with the route or service.

P11. The router of claim P10, wherein the source router logic isconfigured to include the first successive router in the first metadata.

P12. The router of claim P10, wherein the source router logic isconfigured to exclude the first successive router from the firstmetadata.

P13. The router of claim P10, wherein the source router logic isconfigured to include second metadata in the packet, the second metadataincluding session identification information.

P14. The router of claim P10, wherein the controller further includessuccessive router logic configured to:

-   -   receive a packet and determine if the router is the destination        router based on metadata associated with the received packet;        and    -   when the router is not the destination router, forward the        packet toward a next successive router in the ordered list of        routers.

P15. The router of claim P14, wherein the successive router logic isconfigured to remove itself from the first metadata before forwardingthe packet to the next successive router.

P16. The router of claim P14, wherein the successive router logic isconfigured to forward the packet to the next successive router bychanging the destination address of the packet to an address of the nextsuccessive router.

P17. The router of claim P16, wherein the successive router logic isconfigured to forward the packet to the next successive router byfurther changing the source address of the packet to an address of theforwarding router.

P18. The routing system of claim P14, wherein the successive routerlogic is configured to forward the packet to the destination withoutmetadata when the router is the destination router.

P19. The routing system of claim P14, wherein the successive routerlogic is configured to determine a second path to the destination forthe route or service, the second path including a second ordered list ofsuccessive routers to receive the packet associated with the route orservice, and to transmit the packet with second metadata including alist of at least one remaining router of the second ordered list ofrouters to receive the packet associated with the route or service whenthe router is the destination router.

CONCLUSION

Although the above discussion discloses various exemplary embodiments ofthe invention, it should be apparent that those skilled in the art canmake various modifications that will achieve some of the advantages ofthe invention without departing from the true scope of the invention.Any references to the “invention” are intended to refer to exemplaryembodiments of the invention and should not be construed to refer to allembodiments of the invention unless the context otherwise requires. Thedescribed embodiments are to be considered in all respects only asillustrative and not restrictive.

What is claimed is:
 1. A first router comprising: storage media; andprocessing circuitry in communication with the storage media, theprocessing circuitry configured to: compute, based on serviceavailability information for each router of a plurality of routers, anaggregated route for reaching a service, the aggregated routerepresentative of a plurality of routes from the first router to theservice via the plurality of routers, compute an aggregated metric forthe aggregated route; and publish, to at least one other device, theaggregated route and the aggregated metric.
 2. The first router of claim1, wherein the service availability information comprises, for eachrouter of the plurality of routers, an availability of the service viathe first router.
 3. The first router of claim 1, wherein, to computethe aggregate route for reaching the service, the processing circuitryis configured to compute, based on the service availability informationand network topology information for each router of the plurality ofrouters, the aggregate route for reaching the service.
 4. The firstrouter of claim 3, wherein the network topology information comprises,for each router of the plurality of routers, a route to the service viathe first router and a metric for the route, wherein the plurality ofroutes comprise the respective routes via each router of the pluralityof routers.
 5. The first router of claim 3, wherein, the processingcircuitry is configured to compute the aggregated metric for theaggregated route based at least in part on the network topologyinformation for each router of the plurality of routers.
 6. The firstrouter of claim 1, wherein the aggregated route comprises a unitarysegment representative of the plurality of routes from the first routerto the service via the plurality of routers, the aggregated routespecifying the first router as a next-hop toward the service.
 7. Thefirst router of claim 1, wherein to publish, to the at least one otherdevice, the aggregated route and the aggregated metric, the processingcircuitry is configured to publish, to a second router subscribed toreceive the aggregated route and the aggregated metric of the firstrouter, the aggregated route and the aggregated metric, wherein theplurality of routers does not include the second router.
 8. The firstrouter of claim 1, wherein to publish, to the at least one other device,the aggregated route and the aggregated metric, the processing circuitryis configured to publish, to a server, the aggregated route and theaggregated metric for distribution by the server to a second routersubscribed to receive the aggregated route and the aggregated metric ofthe first router, wherein the plurality of routers does not include thesecond router.
 9. The first router of claim 1, wherein the processingcircuitry is further configured to: receive, from a server, serviceavailability information for each router of the plurality of routers forwhich the first router is subscribed to receive the service availabilityinformation; and publish, to the server, service availabilityinformation for the first router for distribution to each other routerof the plurality of routers that is subscribed to receive the serviceavailability information for the first router.
 10. The first router ofclaim 1, wherein the processing circuitry is further configured to:receive, from each router of the plurality of routers for which thefirst router is subscribed to receive service availability information,the service availability information for the respective router of theplurality of routers; and publish, to each other router of the pluralityof routers that is subscribed to receive the service availabilityinformation for the first router, the service availability informationfor the first router.
 11. The first router of claim 1, wherein theaggregated metric comprises at least one of a loss, a latency, a jitter,or a cost for the aggregated route.
 12. A method comprising: computing,by a first router and based on service availability information for eachrouter of a plurality of routers, an aggregated route for reaching aservice, the aggregated route representative of a plurality of routesfrom the first router to the service via the plurality of routers,computing, by the first router, an aggregated metric for the aggregatedroute; and publishing, by the first router and to at least one otherdevice, the aggregated route and the aggregated metric.
 13. The methodof claim 12, wherein the service availability information comprises, foreach router of the plurality of routers, an availability of the servicevia the first router.
 14. The method of claim 12, wherein computing theaggregate route for reaching the service comprises computing, based onthe service availability information and network topology informationfor each router of the plurality of routers, the aggregate route forreaching the service.
 15. The method of claim 14, wherein the networktopology information comprises, for each router of the plurality ofrouters, a route to the service via the first router and a metric forthe route, wherein the plurality of routes comprise the respectiveroutes via each router of the plurality of routers.
 16. The method ofclaim 14, wherein computing the aggregated metric for the aggregatedroute comprises computing the aggregated metric for the aggregated routebased at least in part on the network topology information for eachrouter of the plurality of routers.
 17. The first router of claim 1,wherein the aggregated route comprises a unitary segment representativeof the plurality of routes from the first router to the service via theplurality of routers, the aggregated route specifying the first routeras a next-hop toward the service.
 18. The first router of claim 1,wherein publishing, to the at least one other device, the aggregatedroute and the aggregated metric comprises publishing, to a second routersubscribed to receive the aggregated route and the aggregated metric ofthe first router, the aggregated route and the aggregated metric,wherein the plurality of routers does not include the second router. 19.The first router of claim 1, wherein publishing, to the at least oneother device, the aggregated route and the aggregated metric comprisespublishing, to a server, the aggregated route and the aggregated metricfor distribution by the server to a second router subscribed to receivethe aggregated route and the aggregated metric of the first router,wherein the plurality of routers does not include the second router. 20.Non-transitory, computer-readable media comprising instructions that,when executed, are configured to cause processing circuitry to: compute,based on service availability information for each router of a pluralityof routers, an aggregated route for reaching a service, the aggregatedroute representative of a plurality of routes from a first router to theservice via the plurality of routers, compute an aggregated metric forthe aggregated route; and publish, to at least one other device, theaggregated route and the aggregated metric.